A friend of mine, Jack Kutilek, wrote a web-based player for the CA rules format that I used in Lifelike — basically simple JSON files that describe a state table and the meta-information you need to execute the CA the state table encodes. It uses WebGL and a fragment shader and as such is very fast.
I made a little web page interface here, some cellular automata, which just embeds Jack’s fragment shader thing via an iframe. The naked player is here, running Joe Life by default. You can run it on different rules by providing it URI-encoded Lifelike JSON as an HTTP query string.