Way back in 1999, I wrote a game (in C using raw X-Windows calls! source code) for Linux called XTux. The graphics were made by my friend James Andrews (who recently started a blog on iPhone games)
Some interesting things I remember from the project:
-You could write text strings onto the maps (see Slashdot level screenshot)
-Particle System (see railgun trail and blood splatter in screenshot). One of the most common forms of procedural graphics, now standard in most game engines - this was my 1st implementation and I got a lot of use out of the code (weapon effects, smoke, explosions, blood etc)
-Recording/playing demos was a nice hack: The client was very simple - read messages about what to draw from the server. By taking advantage of the polymorphism in Unix file descriptors, the source could be either a socket connected to the server, or a stored local file of previous gameplay.
-Generating different images (eg preview mini maps) from displaying the same map data in different ways.
-Because the levels were flat text, I was able to easily write a Perl script to generate levels, though I didn't take that beyond generating an arbitrary sized maps of grass with randomly placed trees.
