SuperTux is a side-scrolling platform game. The hero in this game is Tux the Penguin, the game's only reference to Linux. On the journey to rescue Penny, who has been kidnapped by evil Nolok, Tux faces 23 different kinds of bad guys while jumping and running through 101 beautifully-drawn levels. The soundtrack is available on last.fm and similar sites.
PhysicsFS is a library to provide abstract access to various archives. The programmer defines a "write directory" on the physical filesystem. No file writing done through the PhysicsFS API can leave that write directory, for security. For file reading, the programmer lists directories and archives that form a "search path". Once the search path is defined, it becomes a single, transparent, hierarchical filesystem. This makes for easy access to ZIP files in the same way as you access a file directly on the disk, and it makes it easy to ship a new archive that will override a previous archive on a per-file basis. Symbolic links can be disabled, for added safety. Finally, PhysicsFS gives you a platform- abstracted means to determine if CD-ROMs are available, the user's home directory, where in the real filesystem your program is running, etc.
SDL.NET is a set of object-oriented CLS-compliant .NET bindings for the SDL gaming library. It provides high-level access to audio, keyboard, mouse, joystick, TrueType fonts, various image formats, sound mixing, MPEG-1 movies, and 3D hardware via OpenGL and a 2D video framebuffer. It is compatible with both .NET and Mono runtimes.
NRobot is an autonomous robot fighting game. Instead of directly controlling a robot, the human playing the game must write a program that acts as the "brain" of the robot. The robot will then be dumped into the game arena and must attempt to survive on its own. NRobot is written for the ECMA CLR. It's been tested on Mono and on Microsoft's .NET framework. Currently, it is functional and "playable". It comes with three sample robot implementations, so that "out of the box" you can watch a game. One important missing feature is a security architecture: robot code executes with full privileges. Thus, it's recommended that if you are running any robots from untrusted sources, NRobot is run under a user account with no privileges over files you care about. It's also short on documentation, and the GUI implementations have some rough edges.