...: http://sourceforge.net/p/chaosesqueanthologyvolume2/ )
200+ weapons. Build-able enter-able buildings (Like an FPS RPG but with interiors) (Multi-tool/ Utili-tool). City generation (all buildings enterable). A 2 iso (6GB) exploration of what QuakeC can do. Over 100 maps included, along with map editor and sourcecode. Fully free and opensource: code and media.
A modification of Xonotic which included extended weapons, maps, vehicles, buildable buildings, mounted weapons, spell casting, monsters, player characters, textures, and game mode (such as colorwar (think liquidwar))
To pick up items press F.
...