Mac OS X Applications
Snail Mail

Snail Mail is an envelope addressing and printing application which interacts directly with the Address Book database in Mac OS X.

Note that Snail Mail has been discontinued, and is no longer available (unless another developer takes it on).
More about Snail Mail
 
Yum

Yum, the worlds greatest recipe management application, has been acquired by 'Dare to Be Creative'. The new home page for Yum is: http://creativebe.com/yum/