BZFlag is a 3D, multiplayer, tank battle zone, capture the flag game that pits players against each other in a networked environment. It runs on Windows 95/98/NT/2000, Linux, MacOS 10.x, Irix, Solaris, and others. An OpenGL accelerator is highly recommended, but it is playable with 3D in software.
GCompris is an educational software suite with numerous activities for children aged 2 to 10. Some of the activities are game-orientated, but nonetheless still educational. These include computer discovery (keyboard, mouse, different mouse gestures), algebra (table memory, enumeration, double entry table, mirror image), science (the canal lock, the water cycle, the submarine, electric simulation), geography (place the country on the map), games (chess, memory, connect 4, oware, sudoku), reading practice, and others (learn to tell time, puzzles of famous paintings, vector drawing, cartoon making, etc.). It currently offers in excess of 100 activities, and more are being developed.
SecureSkat is a peer-to-peer implementation of the German card game Skat. The program negotiates participating players and game sessions over an arbitrary IRC network (Internet Relay Chat). Neither a trusted third-party (dealer) nor a centralized game server is necessary. All critical operations, e.g. shuffle of the deck, are performed using advanced cryptographic techniques (so-called Mental Poker solutions) provided by LibTMCG. The outdated OpenSkat branch contains a graphical user interface based on XSkat 3.4. This interface can be used with most recent versions, but must be built separately.
Flight Navigation Planner lets you make flight plans based on known airports, navaids, fixes, or cities. You can use the sectional charts, wacs, or the vector/terrain planning charts. It calculates headings, winds, time, and fuel. It features Airways-based Auto-Routing, Climb and Descent calculations (a/c type based), Fuel Stop Planning, Auto-Route around MOAS and Restricted Airspace, Hi-Res Weather Radar Overlay, Viewing of current sectional, wac, and IFR charts, the ability to see a route over TFRs, detailed nexrad radar overlays over your routes, Terrain Profiles with cloud ceilings, and the ability to upload flight plans to GPS.