The Ideas Board placed magnetic LEGO cards onto a magnetic whiteboard. Proposers would write a session idea onto the whiteboard to share it. Participants would place a LEGO onto the card to indicate interest in the session.
For the 2013 Festival of Learning, I helped Sayamindu build an open source, online registration system for unconference festivals, inspired by our experiences at the Mozilla Festival, SourceCamp, and Python conferences.
This project is ongoing. Contact us if you want to use it at your event.