Thomas Fuchs launched script.aculo.us yesterday. In his own words:

script.aculo.us provides you with easy-to-use, compatible and, ultimately, totally cool JavaScript libraries

Check his demos (visual effects and drag ‘n’ drop) even if you’re not into javascript. They are indeed very cool, having a quality usually seen on flash sites.

Moreover, Thomas releases his libraries under an MIT license (do anything you like, but include the copyright notice).