JohnnyVon
JohnnyVon is what I worked at while I was at the NRC in 2003, and will continue to work on for my contract from Sep-04 to Jan-05. Depending on where you come from, it's the Game of Life (The Computer Science one, not the board game) taken into continuous space, or it's a simulation of simplified, semi-plausible DNA.
For scads more information, read Peter Turney's JohnnyVon Page.
All that's available now is one small change I added a long time ago to support a phenotypic state as well as the genotypic state.
The NRC graciously allowed this project to be released under the GNU General Public Licence (GPL).