Two Jamie Zawinski applications, one real and one proposed, that display Intertwingularity.
BBDB (Big Brother Database) http://www.jwz.org/bbdb/ The main feature of BBDB is that it sits in the background and "notices" things about whatever messages you read (in EMacs) (whether those messages are mail or news). A window displaying the address-book entry corresponding to the sender of the current message is always on the screen, unobtrusively. So as you are reading a message, any additional annotations you have made (including ones which occurred automatically) will be readily visible as well.
Intertwingle, http://www.mozilla.org/blue-sky/misc/199805/intertwingle.html for managing lots of EMail. Intertwingle can be seen as a unification of a search tool and an address book. It is not, however, a mail reader. The presentation of query results could be done through a mail reader, but the intention is that ones choice of mail reader should be orthogonal to the use of this tool. The two kinds of tools just happen to operate on the same data.
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