Game of Life
The stuff here is a bit old, but I think some of it is still interesting.
Random Agar v1.1 (released October 2002). This program is intended to look for new Life oscillators, wicks, and agars. It generates random spatially periodic patterns, and runs them until they oscillate. It includes complete support for all possible symmetry types. See the program's Read Me file.
Catalyst v1.0 (released 2001). This program finds ways of modifying the evolution of an input pattern by placing catalysts that react with it, by a backtracking search.
Stable and Glider (released February 2000). What if a glider collided with a group of simple still lifes, generating a glider in the opposite direction, and then the still lives re-appeared in their original configuration? While a little bit unlikely, such a reaction (or a couple of them) might lead to an arbitrarily-slow spaceship or a new stable glider reflector. With this program I tried systematically to find such a reaction, and I didn't find anything (although I didn't exhaust all the possibilities).