FreeCiv - Freeciv is an open-source, turn-based strategy game based on Civilization II.
Particlescape - Particlescape app lets you create stunning patterns at your fingertips.
C-evo - C-evo is a freeware empire building game for Windows
TripleA - TripleA is a free (under GPL) turn based strategy game based on Axis & Allies board game.
0 A.D. - 0 A. D. is a free, open-source, historical Real Time Strategy (RTS) game currently under development by Wildfire Games, a global group of volunteer game developers. Download 0 A. D.
Fluid dynamics - Fluid dynamics developed and published by Reinder Nijhoff.