See the README for more info, and Changes, if you've seen any previous version. The manual is not yet written.
Screenshots: main window (jpeg, 25 kB), message window (jpeg, 25 kB). These are of version 0.2, or something.
You need the Slime source package, my pyliw package (version 0.3), Mitch Chapman's UITools, and Python. Note that version 0.9 of Slime needs version 0.3 of pyliw (older versions had a bug, now fixed).
Message formats:
Protocol related stuff:
Mailbox formats
Other mailers and mail-related software:
Other stuff