This is a 3D action game called knockoff (KO) I've written in C++ using OpenGL. I've been working on it since late June 2003 and its now pretty much complete. I wrote all the code, and did all the art and modeling myself (hence the simple "programmer art" style), but its come together pretty nicely anyway (music was done by a friend of mine). In true cartoon style you have to knock your opponents off the floating platforms any way you can. At the moment its up to 8 players, but only 2 can be human (fitting more than 2 people on a keyboard isn't practical), but I'm working on a networked version so hopefully soon you'll have 8 player deathmatch!
KO runs with over 60fps on my GeForce2 at home and over 200fps on the GeForce4's at my uni. I use no OpenGL extensions (its all done in software), you can turn off almost all features to speed things up, and run it in a mini window if you want so I think it'll run on almost anything with a 3D card (if someone has some old hardware they'd like to test it on I've be interested to see what the minimum specs are).
Current Features include:
Stencil Buffer Shadows
FMod game sound including an MP3 player
Demo recording + playback
Screen shots (can be used with demo playback to output at 30fps to make game movies)
AI for up to 8 players
Lens flares (not because they help, just because I was board one night)
full quake style console
6 game types (including Deathmatch, CTF and King of the Hill)
10 maps (some mod specific)
KO is open source so for anyone who's interested you can get it from my site http://www.kaysik.net. Its cross platform and runs on linux and windows (and theoretically mac, but thats never been tested).