Crystal Game Framework
Crystal allows you to focus on your game, not the details of realizing a realtime experience in the face of lag.
Here is a working demo: http://keithmgould.cf2.nodejitsu.com/
Here is the source to the demo: https://github.com/keithmgould/Crystal-Game-Framework-Demo
Here is a post describing how Crystal works: http://keithgould.com/post/28875536272/realtime-inertial-multiplayer-games-in-html5