Sparrow is a minimalist mail application for Mac. It was designed to keep things simple and efficient.
The current beta only supports Gmail; however, there are plans to bring IMAP support and more.
The user interface is similar to Tweetie for Mac.
FEATURES: ● Threads: Quickly flick through threaded conversations on your mac like never before. ● Not so minimal: See your mails the way you want. Quickly glance at the preview. Read it in a new window or open the right pane to enjoy Sparrow's full potential. ● Notifications: Growl is integrated for notifications addicts. ● Multiple Accounts: Seamlessly switch between your mail accounts.