The vast majority of video games can be said to fall into one of two groups by the way they deal with the flow of time.
The first group is turn-based games, which play like chess or monopoly: The game is sliced into pieces so that each player can make decisions, give commands, and watch those commands being executed without interference from the other player(s).
The second group is Realtime games, where time never stops for anyone: All players are interacting with the game simultaneously, and everything happens all at once. Quick thinking and quick fingers can, depending on the game and/or player, become a key advantage.
While games within each group can be very similar to one another in terms of style and design, Realtime and Turn-Based games tend to be very different from each other. Turn-Based games put an emphasis on thinking ahead and analyzing your best move from a wide array of choices, while Realtime games put an emphasis on quick-thinking and motor skills with a streamlined interface. As a result, these two groups often appeal to different kinds of players.
Over the course of the years, there have been many diverse and sometimes very successful attempts to combine aspects of both groups into a single game. The intended result is usually to keep the smooth pace of Realtime games, while allowing for more forethought and elaborate interfaces as in Turn-Based games. The hybrid is then said belongs to the category of Realtime With Pause games (RTWP, or Pausable Realtime [PRT]). In some cases, the hybridization simply makes a fast game more accessible to slower-fingered players.
Approaches to this issue are often unique or innovative, as there are many possible combinations to be tried. Games may have a different emphasis on action versus strategy, and interface design can make a huge difference too. Playing without the pause aspect can be a form of Self-Imposed Challenge, assuming the option is even available at all and does not make the game unplayable.
RTWP games can generally be categorized into one of the following groups:
Plain Realtime With Pause: The game runs in real time, which means that all characters and enemies are constantly active. Players can give commands whenever they wish, just as in regular "Realtime" games. However, when the game is paused, the player retains his/her ability to give orders, survey the playing field, and pretty much do anything that's possible when not paused. Any orders given by any player while the game is paused will be executed as soon as it is unpaused. The main goal of this design is to allow players to stay "on top" of the situation, reducing the need to frantically move the mouse or controller all over the screen to get their bearings. It also allows issuing complex orders to multiple characters and digging deep through complex menu systems, which would otherwise require very fast fingers.
This type of gameplay is usually only available in games where one human player is facing off against one or more computer-controlled opponents. If the game also has multiplayer mode, the option to pause is normally disabled completely in that mode.
Since "Realtime With Pause" often relies heavily on some degree of automation between orders, Artificial Stupidity may become a problem, so the ability to issue some kind of simple conditional commands is common - sometimes amounting to a simplistic Programming Game.
Simultaneous Turn Resolution: This is an approach more similar to Turn-Based games. It involves two distinct phases: the Command Phase and the Execution Phase. In the "Command Phase", all players issue orders to their characters simultaneously, usually within a limited amount of time. Once everyone's done giving orders, the game goes into the “Execution Phase” where all of the orders are executed simultaneously, while the players can only sit back, watch, and hope they made the right choices. Rinse and repeat until one side has lost. Essentially, this can be seen as a "forced" pausing of the game at regular intervals, instead of simply allowing players to decide when to pause. Since pause is enforced (and its duration usually limited), this is a suitable design for both single-player and multi-player games.
This style of gameplay attempts to circumvent one of the major grievances with traditional Turn-Based games, where one team moves or acts while the enemy characters can only stand around like dummies while waiting for their next turn to begin. Simultaneous Turn-Based games are especially advantageous for multiplayer, because the game takes the same amount of time to play no matter how many participants there are.
In single-player games where there's only one entity under human control, this is commonly used to brush unimportant NPC movements under the rug, such as in Roguelikes and non-combat mode in many RPGs.
When this method is used in strategy games, any combat erupting between two units during the Execution Phase is usually resolved entirely by the AI. This takes away the advantage over AI that human players usually have with tactical micromanagement (thanks to Easy Communication), which developers may see as not justified if your Non-Entity General is not supposed to be available on the battlefield. Since automatic resolution may make Artificial Stupidity highly frustrating, some games allow rough control via standing orders for units or groups of units, such as generic behaviour (all-out attack / try to keep at the longest weapon range / run away) and/or target priorities (burn the fuel carriers first, to get 'em all stranded).
Simultaneous Turn Resolution With Pause: As above, but combined with something like the ATB system from a Final Fantasy game. The game feels like a Realtime With Pause game, except in truth it is actually a well-disguised Simultaneous Turn Resolution game. In this design, the game appears to runs in real time: It runs by itself when unpaused, orders may be given and the game paused at any time for giving orders. However, all actions start and end in unison, any order given (whether in paused or un-paused mode) is only executed once the next “turn” begins, and actions can't be interrupted or cancelled before they finish.
Unintentional Realtime With Pause: This is a special case. The designers only added the ability to pause the game as a simple convenience (allowing the player to take a break from the action) - which is obvious since the screen goes grey and/or a big obtrusive box appears, saying "The game is paused". But while the designer intended the game to be truly paused while in this state, for some reason it is still possible to examine the playing-field and/or give orders to your units!
Other designs: Since the number of combinations between Turn-Based and Realtime features is only up to the designer's imagination, it's not surprising that some games feature a combination that's never been done before.
Note that the majority of RTS games, like the Command & Conquer and WarCraft series, do not allow PRT gameplay, but do allow slowing game-speed to a crawl. This achieves roughly the same purpose, making the game more manageable for players with less manual dexerity.
Nearly all BioWare and (to a lesser extent) Obsidian titles, as well as games made using engines licensed from them:
With one (intentional) aversion in the original's single-player mode, where the entire game and all its menus respect the game's pausing...except for the inventory screen, which causes the game to unpause in the background, while you can't see anything. However, starting a single-player game as a multiplayer one bypasses it.
The game is designed in a way that makes it much more difficult to play without any pausing. This is because, while paused, a menu slides open allowing all sorts of commands that aren't otherwise available, even with hotkeys.
Except while aiming the sights down for a sniper rifle, presumedly because constantly pausing to line up easy shots with them would just be unfair.
The Dragon Age series: On any difficulty higher than Easy, it is absolutely necessary to pause in between actions to assess tactics and make decisions.
King Arthur The Roleplaying Wargame even allows you to speed up the game during moments in battle where you will decisively win or nothing will happen for a while, slow the game down for tenser moments to better analyze and micromanage your troops as well as using skills, in addition to just pausing it.
Achron is a rare multiplayer version of this kind of game. Since it's a time-travel strategy game, it can accomplish this by allowing the players to pause time but not pause meta-time. Even if you do freeze a moment to give your units complex orders, you better be quick because your opponent is still somewhen out there mucking with the timeline.
Dwarf Fortress is a special case since you can't actually give orders while the game is not paused. Whenever you go into any menu to give orders, the game pauses. Good thing, too, otherwise the game would be nigh impossible. In Adventure Mode it pauses every time your character is allowed an action, skewing the line between this trope and an extremely complicated turn-based game.
The battle portion of Total War games. The strategy portion is purely turn-based. However it's subverted in the highest difficulty of Shogun 2, as it removes the option to pause, in addition to a large number of other handicaps in order to make the game more difficult.
The RollerCoaster Tycoon series is a strange example. In the first two games, anything can be done while the game is paused, except for construction of any kind (removing scenery, adding rides, adding paths, etc). Basically, everything useful. You can even pick up people and place them wherever you want to, and they will fall back to the ground when the game is unpaused (helpful when you "accidentally" put a lot of people into a body of water). The third game, however, allows full control of the game while paused.
This is justified in that, for the first two games, your objectives are usually more based on time (I.E. 1000 guests by the end of year 3) so being able to do everything without time constraints is an unfair advantage. For the third game, the scenarios' objectives are almost always completable at any time, and for events that only occur on certain days, they will continue to occur until you complete the objective.
Unfortunately, paused mode only allows some commands, while others require the game to be unpaused - like picking people up or relocating/deleting scenery objects. Due to the fast-paced nature of the game, this renders paused mode useless for virtually anything except examining the situation (which is still very very important).
Nexus: The Jupiter Incident
The Tropico series, although in some cases (such as commands to El Presidente), you won't see the nature of the most recent order until you unpause. The game will also autopause at some points, such as when using menus or laying down roads.
7.62mm High Caliber (or 7.62 High Calibre), a Spiritual Successor to the Jagged Alliance games, uses this system for combat, though the gameplay can be slowed down too; each character has an action queue with actions' time to complete measured in the hundredths of a second, such as taking a shot (such as snap, aimed or scoped), or weapon transitions, readying a grenade for throwing, the actual throw, and so on. Unfortunately since the orders themselves are not displayed, this can lead to some awkward or time-consuming moments, especially when rearranging gear in one's vests, pouches, holsters, slings or backpacks during combat.
There's also the extremely annoying tendency for certain actions that, once started, cannot be cancelled, like reloading a weapon (which can take a very long time if you don't have a spare clip).
Most SimCity games have four speeds, including Pause. No control is lost in the paused state, allowing the mayor to change the entire city in the blink of an eye in their population's perspective. The only exception is during a disaster, wherein the player must resolve the crisis in realtime.
The "Pause" button on Captain N's Controller is like this... for his allies. Kevin is fully mobile during the pause effect and can relocate objects... but can't give his friends new orders.
Galaxy Angel, being closer to a real-time tactics than an RTS, allows for pause for you to input your commands at your leisure. However, you don't even need to do that, as time is temporarily paused while you enter commands anyway.
The Sims and its sequels — though the game is deliberately designed to be easy even without the pause feature.
Vandal Hearts 2 uses the Dual-Turn Battles, which is this to a tee. Not only you need to move your characters, you need to anticipate which enemy character will move, to where, and what action will they do. This requires a lot of advanced thinking and good guess, even if the AI can be abused to allow unlimited turn treasure hunting.
In the game, there even exists a spell called "Premonition" which tells you which enemy character will move. However, it will not tell you where it will move and what it will do. An experienced enough player can still make educated guesses based on the enemy's movement range, weapon range, skill and equipment list, etc.
During space battles, the game pauses at the beginning of each "day". You choose a direction to fly, as well as which weapons will fire at which target. Then unpause, and watch all spaceships in the battle duke it out simultaneously. Correctly anticipating where the enemies will end up at the beginning of the next day is crucial.
Critical Mass has a similar system, though on a much smaller time scale.
Naval combat in Puzzle Pirates is simultaneous turn-based. In fact, it has one "command phase", and four consecutive "action phases". During the command phase, the ship's Battle Navigator has to input four actions, anticipating where the enemy ship will be in each of the four stages. Firing or moving in the wrong stage can lead to loss of ammo and/or unwanted collisions!
This gets even more complicated when the Battle Navigator is trying to rig the sails or load the cannons at the same time (both are furious action-oriented puzzles requiring a lot of skill and concentration!). Some captains are so good at this, they can sail a ship with half a crew on-board, filling in themselves during intense battles
Roguelikes: The game is normally in Paused mode. Once the player inputs a command (only one) for his character, time will move forward exactly as long as required to perform the selected action. Then the game is paused again, waiting for the next command. If your character is heavily burdenned, this means you can be dogpiled while taking a single step, or visa-versa.
Outside of combat in games like the Ultima or Exile series, the entire thing in others like Might And Magic or Cythera, where you can only control a single character at a time.
BattleTech the board game does this — the players move or fire one unit at a time alternating between them. In the case of weapons fire, all effects take place at the end of the phase.
Global Conquest on the PC version of Kane's Wrath, until a battle occurs for which the game switches to RTS.
While Civilization is more or less uniformly straight-up Turn-Based Strategy, multiplayer games can be played with simultaneous execution. This is useful when there is a large number of players in later stages of the game: Turns in single-player games can easily take as much as half an hour, particularly if the player's empire is large and at war. Imagine, then, that you have four or five human-controlled large empires, all at war. Yeah, you'd like simultaneous execution, too.
The space strategy game Flotilla is basically exactly that. You usually only have 2 to 5 units and order every single one of them to move somewhere on the 3D grid, shoot at an enemy (or not) and turn, tilt and roll over during the execution phase. This precision is needed since they all have ridiculous armor on the front and the top and are very vulnerable at the back and the bottom.
The ragdoll fighting game Toribash has a unique way of using this system. Two players face off in one on one matches controlling all the major joints of their respective ragdoll. At the beginning of each turn players have a limited amount of time to manipulate the joints of the ragdoll in order to get it to move. After which the ragdolls move as predicted a small amount and the process repeats. Through careful planning and manipulation, the ragdolls can be made to do virtually anything.
Another classic non-video-game example is Diplomacy (from the same company as the above game, Avalon Hill). This combines—or perhaps conspires—with the totally deterministic battle system and various other features to make the game an excellent exercise in the Gambit Pileup.
Master Of Orion. MoO 2 has Simultaneous Turn Resolution either interrupted with classic turn-based combat if its tactical mode set to manual, or AI (not really smart, nor indirectly controllable) resolved combat.
VGA Planets was one of the early 4X games using Simultaneous Turn Resolution.
Stars!, as a Spiritual Successor of VGA Planets. Fleets have a "Battle Plan" set for possible encounters, independent from the current mission and customizable, including priority targets and basic tactics.
Examples of Simultaneous Turn Resolution With Pause
Star Wars: Empire At War has a tiny, hard-to-reach pause button with no hot-key associated with it. It clearly was not intended (or at least badly designed) to pause the game often enough in mid-combat for it to be useful. There are third-party mods that add a hotkey, making it a viable feature. Considering the quick pace of battles in this game, it is not surprising that such mods were developed. Some players consider this cheating, however.
The first Homeworld game has a pause feature which actually makes the game more difficult to play because its behavior is very unpredictable. It may have been designed to allow examining the battlefield, but not to issue commands. Still, some players do manage to use it that way, making the zero-g RTS significantly easier.
This is very common in fast-action and arcade games across all platforms, if the pause feature allows the player to examine dangerous situations while they are frozen. Naturally, it only applies if examination of the danger confers a significant advantage to the player once the game is un-paused. Many players consider this cheating. Others simply say it's a way to play the game if you lack the twitch-reflexes normally required. Naturally, this does not apply in multi-player mode where pausing is almost always disabled anyway.
One type of game that's especially prone to this are Tetris and its clones, which now usually cover up the board when pausing. A variation peculiar to them is “infinite spin,” in which a player spins a piece simply to stop it falling.
Hidden Object Games are often timed - whether counting down (as a deadline) or counting up (for scoring purposes). Given the vast number of such games made in the past decade, you're absolutely bound to come across a timed game where the designers hadn't really considered this exploit. So when the game is paused, the scene remains quite visible (sometimes simply a little darkened) and you can actually keep looking for clues without wasting any precious time. This has recently been changed a little, due to many Hidden Object Games abandoning the time factor altogether.
But it does persist in other casual games like the "connect 3" variety, especially since there are so many of them being made.
Examples of other designs:
Fallout 3 has V.A.T.S mode, where the game is paused mid-battle, and the player can target an enemy's bodyparts. This is unique in that once unpaused, the game goes into a slow-motion replay of the shooting sequence that was queued in V.A.T.S, temporarily taking away the player's control of his character. The game then proceeds right back into full realtime mode.
The Clue and The Sting. These games use a Simultaneous Turn Resolution design, except there's only one "turn" in each mission. You can spend up to an hour giving a long sequence of commands to your team members, and then watch the heist being performed in real time with no opportunity to intervene until it's done.
Similarly, but more extreme, the Dominions series. You can only input general commands to units when you organize them, and must have faith in those orders working when combat occurs, whether because you initiated an assault or were attacked.
The Matrix: Path of Neo. The pause screen gives 'Neo' the 'see everything as vertical lines of numbers' ability. Including seeing enemies hiding behind nearby walls.
Several adaptations of the board game Space Hulk use a restricted version of Real Time with Pause called "Freeze Time." During normal gameplay, you can control troopers directly or give them orders on a map screen. If you activate Freeze Time, the game will pause and go to the map screen, where you can continue to input orders that will be carried out once you go back to normal gameplay. The big difference is that the amount of time you can spend in Freeze Time is strictly limited, with a meter that ticks away and dumps you back into normal gameplay when it runs out, and only very slowly refills during normal gameplay. The overall effect was a use of Real Time with Pause that actually made the game more intense.
James Bond: Everything or Nothing has the "Bond Sense" mode, which allows the player to replicate Bonds expert markmanship by both giving them more time to examine the situation and select targets, and also highlights enemies and destroyable scenery. While it doesn't fully pause the game, it does slow the action to a crawl to give you more, but not unlimited time.
The Inazuma Eleven series straddles the line between plain Real Time with Pause and Simultaneous Turn Resolution. They're primarily plain Real Time with Pause, with the caveat that the manual pause has a 10-second cooldown after resuming before it can be used again. However, some events will trigger an automatic pause (not subject to the 10-second cooldown); if the event in question requires the player to choose one of several actions (for example, an opportunity to steal the ball: regular tackle or sliding tackle?), it gets Simultaneous Turn Resolution.
In the Grandia games, it pauses for special attacks and when character actions are to be selected, but otherwise the battles move in real time.
Resonance of Fate bills itself as being turn-based, but plays more like a blend of Realtime With Pause and Simultaneous Turn Resolution. At the start of PC's turn, you have as long as you like to switch weapons and targets, looks around, or change to other PCs with a turn pending. The moment you move an inch or change an attack, however, enemies start carrying out their turns, and continue to do so even if you stop performing actions that drain your action bar. Once the player ends their turn by taking a shot or emptying the action bar, any enemies with attacks readied get to launch them, then action moves to the next PC (enemies never get dedicated turns, but all of them attack every PC turn).