Pybik is an interactive, graphical, single player puzzle about the cube invented by Ernő Rubik. Besides the cube, the program can handle towers and bricks (non-cubic puzzles). Pybik also has solvers, pretty patterns, and a collection of various moves. The cube can be manipulated with the mouse or keyboard. You can change the colors or images on the faces of the cube.
Arx Libertatis is a cross-platform, open source port of Arx Fatalis, a 2002 first-person role-playing game developed by Arkane Studios. Arx Fatalis features crafting, melee and ranged combat, and a unique casting system where the player draws runes in real time to effect the desired spell. The Arx Libertatis source code is based on the publicly released Arx Fatalis sources. This does however not include the game data, so you need to obtain a copy of the original Arx Fatalis or its demo.
Liquid War 6 is an original multiplayer wargame. You have to control an army formed with thousands of pixels that look like liquid, and try and eat your opponent. This is a total rewrite of the (now quite old) Liquid War 5 version. It's still in beta stage, with many imperfections and no network play but it's playable now.