- One of the project showcased at node.js meetup:  http://coffeelottery.com/ (right now "problem" of whos making a tea is solved, for me it's actually a pleasure)
-  Another service that brings real-time communication to life: http://pusher.com/examples
-  The standard is being established now: http://en.wikipedia.org/wiki/WebSocket (even most modern browsers does not support it fully)
-  But there are some hacks to have it working - WebSocket emulation - Javascript client - http://sockjs.org
-  Another fancy stuff: http://en.wikipedia.org/wiki/WebGL (a guy built working app within hours: you go to website and if someone is browsing with mobile device you see his lightsabre moving)