ImapArchiver is a tool which can be used to save the all imap account into a local directory/archive. The ideal objective is to used it with cron to automatically make a back up of your imap account
Bahrein is a Perl script that allows you to chat over AIM through only e-mail. All incoming IMs are forwarded through GMail to your destination - and you can reply just as easily back through e-mail to IM again.
MailDB adds a database back-end to an IMAP server for features such as "virtual" mail folders (msgs appearing in multiple folders), "view" folders (dynamic results of searches), etc. The DB is inherently multi-user, allowing msg reference counting.