Video Game / SPACE TRAVEL!
, written by Ken Thompson on a Multics system
in 1969, is a Top-Down View
2D Simulation Game
of flight around our solar system. You fly a spaceship, flying to and landing on the planets and their moons. It's a Wide Open Sandbox
with no goals or enemies. Just fly around. Each planet and moon exerts gravitational pull on your ship, changing its trajectory. Sizes, masses, and distances of of the planets and moons are all depicted realistically. Planets and moons follow orbits, but not realistically; the orbits are perfect circles and all on the same plane.
It's of historical interest because Thompson and Dennis Ritchie invented UNIX
to port it to an unused DEC PDP-7.
Space Travel provides examples of: