Web 2.0 apps...

This will be a long-running series... there's some *really* nteresting applications popping up.

Ning makes it incredibly easy to set up any kind of collaborative space, in moments.
Link: Ning - Create and share your own social web apps!.

Nabble http://www.nabble.com/ puts community groups into a very easily searched, cross platform, free service. Which, if nothing else, would get around the horrendous security barriers that some services (Yahoo! Groups) put up.