Simply the world's coolest WebApp. More-than-HyperCard for the 21st century courtesy of AviBryant. Watch http://www.dabbledb.com/utr/ and ask yourself what the hell you're doing with your life.
On 21 June 2010 DabbleDB has announced that it was acquired by Twitter. No new developmens, no new users anymore.
Now totally dropped by Twitter; no source code released, entire project wiped out. Textbook example of why closed-source web-based "cloud" solutions are dangerous for their users.
See SeasideFramework.