Simulators

Tennix is a single and multiplayer 2D tennis game. A free and open source game

TrackMania Nations Forever is a free multiplayer online racing game

BillardGL – free and open source 3D pool game for one or two players

X-Moto is a free and open source multiplatform 2D motocross platformer game, a 2D motorcycle trial simulator

Frets on Fire is a free and open source multiplatform game where the player simulates the performance of a musical composition using the keyboard