Achilles Life Simulator
Watch a simulation of artificial life and evolution

ACM
turn-based space empire and galactic conquest computer game (client)
Billard-GL
Play Billard Game
CRRCsim
A Model-Airplane Flight Simulation Program

FGo!
A simple and fast front-end for FlightGear Flight Simulator
FlightGear Launch Control
Launch FlightGear via FGRun

FlightGear
Practice flight training (airplanes, helicopters...)
FooBillard++
OpenGL Billiard Game

gl-117
An action flight similator

Lincity-NG
Plan and build a city and take care of transport, economics, electricity and others.

Micropolis
A real-time city management simulator

Oolite
An OpenGL Elite-like space game

OpenBVE
Train/railway simulator compatible with 'BVE Trainsim' routes

Simutrans
Transportation simulator

TORCS
3D racing cars simulator game

Endless Sky
Space exploration and combat game

FlightGear Launcher
Graphical front-end for launching FlightGear flight simulator
Minetest
Multiplayer infinite-world block sandbox

Emilia Pinball
3D pinball game
Planets
A simple interactive program for playing with simulations of planetary systems
Endgame: Singularity
Simulation of true AI

XBall
simulate bouncing balls in a window

CorsixTH
Open source clone of Theme Hospital
Speed Dreams 2
The Open Racing Car Simulator

Billiards
A cue sports simulator

Greyhounds
Greyhounds is a greyhounds racing and breeding game

Kbilliards
Funny billiards simulator
Pioneer
A game of lonely space adventure
Vega Strike
3D OpenGL spaceflight simulator

xgrav
Simple physics simulation

OpenRCT2
Open Source re-implementation of RollerCoaster Tycoon 2.
Powder Toy
Physics sandbox game

Voxelands
3D Voxel World Game

Julius
Open Source re-implementation of Caesar 3.