clay.io
Posted: Tue Jul 15, 2014 4:26 pm
I haven't used it myself, but I have come across quite a few games that implement it so it must be doing something right.
However, I do believe it is more focused on 100% client-side HTML5 games. If you were making some kind of MMO, online strategy game, etc., you would probably be better off implementing something server-side.