Ning
Ning looks interesting. It's a site that lets anyone build their own mashups.
I hate the term mashup. But I hated the term blog, and look where that got me.
So here's the Ning developer documentation.
One innovative idea that they have is that while anyone can log in and work on something from scratch, there are alos a number of simple existing applicaitons that you can simply clone. The web interface makes it easy to take any existing app, clone it, and then use it as the starting point for your own app.
This is an awesome way for folks to experiment with web technologies, and instantly create something they can show their friends.