KataSpace is a new web-based MMO architecture just launching today, a project from Linden Lab alum Henrik Bennetsen, which I wrote about last March. It's a WebGL/HTML5-powered 3D space using Sirikata, a BSD open source-licensed virtual world Henrik helped develop when he was at Stanford's Humanities Lab. You can enter KataSpace now: First, download Firefox 4 Beta, which comes with WebGL, then log in here: kataspace.sirikata.com.
As you can see above, KataSpace is just a rudimentary space with a couple male and female starter avatars (“I like to joke that they’re Adam and Eve”, Henrik tells me), but it should be enough to see the giant potential Henrik and his team at Katalabs have just unleashed: