After private and pubic beta sessions, the Iconfactory today announced the availability of the latest edition of Twitterrific for Mac OS X. Version 2.1 of the popular Twitter client adds several new features and improvements including: Keychain support for multiple Twitter logins; Growl support — Tweets can now be processed with Applescript; UI window customization for transparency, font size, etc.; and more. Twitterrific is offered as freeware.