Sparrow is an attempt to get away from supercomplex, feature-packed e-mail clients in favor of a simpler e-mail experience. The interface is elegant while remaining very straightforward: the left side of the interface shows where e-mails are from, and the right side displays the message and any photos or other media commonly sent through e-mail. Setup only requires that you add accounts; then you can get started right away.
Though the interface is sparse compared with many big-name e-mail clients, you still get plenty of the common actions and options you'd expect from a basic e-mail app in Sparrow. You can save your draft e-mails; "Star" (or mark as favorite) specific conversations; add color-coded labels (which you can later sort by); and quickly open and collapse individual e-mails from a thread. You can also import Facebook pictures for your contacts, get Menubar notifications when you receive a message, and send quick replies. Sparrow offers support for all IMAP accounts, including Gmail, MobileMe, Yahoo, and custom IMAP accounts, and you can set up multiple accounts and view your messages in a unified inbox.
Overall, if you're looking for a desktop e-mail client that's not overloaded with features but keeps some of the most important ones you already use, Sparrow might be perfect for the job.