Correo
Introducing Correo, a new open-source mail client for Mac OS X. Correo blends technology from two popular Mozilla projects, Camino and Thunderbird, to create a polished native Macintosh application.
There are many planned features for the mail client, including plugin capability (to allow development of extensions such as PDA synchronization), tabbed window interface, address book support, keychain access, and various other to-be-determined features.
Correo