Sandcastle Builder is an Idle Game by one Eternal Density as a fan-made companion to xkcd: Time. It was first available on September 4, 2013. The goal of the game seems simple, but isn't. You start out with a clickable image of a beach from xkcd: Time. One click digs one sand, and one sand produces one castle. This seems straightforward, but the amount of sand needed per castle increases following the Fibonacci Sequence. Once you've accumulated enough castles, you'll be able to purchase tools which produce sand automatically, other tools to produce castles at certain intervals, and boosts which let you produce sand and castles even faster. Soon you won't need to click to dig sand manually, but there quickly becomes other reasons to click. Then things get more and more complicated with 'redundakitties', 'ninja', 'the Department of Redundancy Department', 'Judgement Dip', and Time Travel. Also the whole thing is packed full of obscure references and made up words from the xkcd forum.
Sandcastle Builder contains examples of:
- Call a Rabbit a "Smeerp": many words are replaced with counterparts from the xkcd: Time forum thread, just to add "flavour":
- The word "day" is always replaced with "dip".
- Molpies are just cute animals.
- Vital game functions such as "partial reset" and "complete reset" are confusingly named "Molpy Down" and "Coma."
- "big" is replaced by "seaish."
- The numerical value NaN (Not a Number, which results from undefined operations such as subtracting infinity from infinity or multiplying infinity by 0) is displayed as "Mustard."
- Maximum finite value for anything is 1.7976931348623157e+308 - anything higher causes the value to become Infinite. This is a feature of 64-bit floating-point notation.
- Production Control can't be upgraded past 6e+51 at which point the player is awarded the "Nope!" badge.
- Department of Redundancy Department: Literally — they're a group of kittens with neckties who provide you with new technologies.
- Guide Dang It!: The games progression goes all over the place. In many places you can end up putting in effort into an area that would be trivialized though other means, while others, doing that painful process to push just an inch more will unlock a useful boost.
- Mini-Game: Logicats, which involve solving a boolean logic problem, and the "Monty Haul Problem".
- Minus World: intentional example: instead of completely plugging a glitch with Temporal Rift, the developer made it a portal to the 'Minus Worlds', which have their images and text flipped.
- Monty Hall Problem: Played with: the rules as to whether a goat is displayed to the player are hidden to make analysis 'hidden', plus you get to collect goats. To add to the confusion, in-game it is named "Monty Haul Problem".
- Monty Haul: Once you have infinite Sandcastles, you're only getting started.
- Panthera Awesome: Inspired by 'Lucky', the big cat in xkcd: Time, are the 'Not Lucky' reward, and boosts such as 'Panther Salve', 'Panther Poke', and 'Panther Glaze'.
- Save Scumming: It is possible to save and reload the game at certain points to get the best result, or at least avoid a negative one (e.g. if you have enough goats, you can reload to recover lost castles.) However, save scumming is countered by gradually increasing the price of the Monty Haul Problem.