Many different experimental games tied together within a common game. You must beat one game before you can move onto the next.
Approval was a game idea born out of the need/want to prototype games. The idea being that instead of committing to a single game idea we could work on a variety of smaller games. This reduces the development fatigue.
The first phase was started by Garry, ran for a couple of months, and not much got done. It was eventually abandoned as Rust took priority.
The project was started from scratch by Ryleigh who added a bunch of new games. One of the games created was Space Usurper, which eventually took most of his time and approval was once again left abandoned.
Garry returned to the project and decided to start from scratch. Not much progress has been made.