Beagle is a framework for searching and metadata on the desktop. It grows out of NatFriedman's Dashboard and is currently being hacked on by JonTrowbridge, DaveCamp, JoeShaw and others.

You can learn more about Beagle on the Beagle Wiki: http://beagle-project.org/Main_Page

Also, check out Planet Beagle at http://www.PlanetBeagle.org.

We are developing a new ThunderbirdBackend for use with beagle, that has its own page here.