If you need to shift the date or time on a Linux or Unix machine you may be interested in dateshift, a date/time testing tool for Linux and Solaris.
You can find out more about my involvement with free software.
My final year project whilst at the University of Warwick was an Atari 2600 emulator, which I released as open source. I no longer develop it due to lack of time, so to play 2600 games I recommend Stella, as it is faster and supports more games.
For historical interest or if you are looking for a pure C 2600 emulator to port, check out the Virtual 2600 Home Page .
You may like to try a couple of games I have written. Be warned that they are now rather old...
This was included in RedHat Linux 2.1. It is an invaders style shoot 'em up game for linux using SVGAlib, has sound and joystick support. Probably quite hard to compile these days
A tetris clone for DOS with simultaneous two player support. Or for 256 colour goodness get A later version in Mode-X . I prefer the original version myself. Someone even wrote up a nice review of it. Runs quite well on DOS emulators.