New Garageband Killer uJam is the best web app of 2011 — from Cool Stuff for Nerdy Teachers blog

Excerpt:

Ujam is without a doubt the best free app I have seen pop on the web in the last 12 – 18 months and it is a really fresh and unique piece of software that is going to blow your students minds.  Essentially uJam let’s anyone create a professional piece of music in minutes by simply singing.  No instruments required. ( You must see the video below to believe it.)

Ujam