xlife is a laboratory for experimenting with cellular automata. It supports loadable rulesets and palettes, different topologies, and up to 256-state cellular automata. It has rules and patterns for Life, Brian's Brain, Perrier's Loops, Langton's Ants and Loops, Wireworld, E.F. Codd's 1975 UCC automaton, some Prisoner's Dilemma games, and many others. It is very fast for step-by-step mode, bounded grid, and chaotic patterns. It has several unique features: a historical mode, a pseudocolor mode, and n-state statistics. It has been developed since 1989. The modern version of Xlife began its history in 2011.
ca-ga is a toy artificial life simulation that uses genetic algorithms on large cellular automata. It uses simple but easily extended DNA that is 8k long by default, though you can take the size out to anything you have time to evolve. It sits under each cell of a 128x128 board and orders operations to transfer energy in the hopes of achieving a kill and breed. The simulation features a mutating fitness function, emergent sex, and a proof of concept real world fitness function. After enough generations, the cells or genes could achieve collectivism and organismhood, coordinating the values of the hotspots that determine board temperature in order to maintain a desired equilibrium. But maybe not. If you work in a fitness function, an optimizing problem solver results.