I watch (follow) three.js on github for a while and I see frequent activity (commits, pull requests) on the project. Compared to most of the other (2d, simple stuff) frameworks this one is a full blown 3D engine albeit it does only rendering (no collision detection etc).

Made by Mr.doob who did the demos at http://mrdoob.com/ and who worked on Google's http://www.thewildernessdowntown.com/ .

Very cool - I agree 100%