Since you mentioned Spacewar in a post about an MMO, I feel like I need to plug http://www.mmospacewar.com which is a fork I made of MMO Asteroids (featured here as the top post about a month ago) to make it behave more like Spacewar. It isn't fully polished yet (I'd like to use better sprites, the energy costs may need some tweaking, and I'd like to improve support for choosing instances), but it is functional and you and others might find it interesting.