This is Grendel -- a Java mail/news client.

The grendel.storage.intertwingle package implements some of the ideas in
<http://www.mozilla.org/blue-sky/misc/199805/intertwingle.html>.

There are lots of spiffy ideas in intertwingle but the one focussed on
here is just to keep a global database optimized for interesting
searches across all folders.

See http://www.mozilla.org/projects/grendel/ for more info.