For many years Blender (the crossplatform Open Source 3D modelling/rendering package) has had a very unrefined ability to make games. Only recently, with many rewrites and the integration of the Bullet Physics Engine, are we starting to see some real potential for coolness.
The advantage of using Blender (in addition to the whole it-being-free thing) is that the creator can model, animate and script all within the same package. None of the entrants are particularly great games, but the winner, Club Silo, is the most visually impressive Blender game project to date.
For a quick overview, one can view the YouTube Video of the entrants. To play or edit the games, the latest version of Blender is required. Load up the desired game’s .Blend file into Blender, hit CTRL+UP in the game window and press P to play. Recommended more for developers than gamers atm.