Mailsmith is an old-school, text-only email client from Bare Bones (of BBEdit and Yojimbo fame), that has long had a cadre of devoted users, but which has also really been showing its age of late (version 2.1.5 was released in March 2005). Yesterday, however, Bare Bones' Rich Siegel announced a public beta of Mailsmith 2.2 that brings the application into the Intel age as well as adding a variety of other changes, including substantial changes to disk storage formats which preclude downgrading back to 2.1. Siegel emphasizes that 2.2 is not yet for sale and is completely unsupported, but if you're an old Mailsmith user who moved away in the Intel age you may want to check out the announcement.
[Via Daring Fireball]
Update: fixed links to the announcement. Here's a FTP link to the demo of Mailsmith 2.2 (via Hawk Wings)