Wow - 92 apps got made in this years (2007) Rails Rumble (formerly known as Rails Day). The quality, quantity, and functionality are all superior given that these apps were all created in a mere 48 hours!
My favs:

• Invent a Story
  Collaborative story writing - 1 sentence at a time
• This Vs That
  Dual threaded lists perfect for debating
• DuctTape
  Create and publish simple lists/databases
• Researchr
  Group together ideas for a research paper in a drag and drop manner

Rails Rumble goes a long way to showcase the power of Ruby and Rails. In coming weeks I’ll be writing a few tutorials on using Rails to create e-learning/social collaborative apps. Remember that someday soon Rails apps will just deploy on a Tomcat instance - hint hint - Blackboard.