RetroArch is a frontend for emulators, game engines and media players.
A promising chess program
Free 32/64/16-bit multi-platform Pascal and Object Pascal compiler
A cross-platform interpreter for many point-and-click adventure games
Very Powerfull Crossplatform Qt Based Music Note Editor[Still Planing]
Nurikabe, a great game.
Java based Open source Voxel Engine for RTS games