Sparrow is a free Gmail client for your Mac that was released yesterday and is still in beta. Unlike MailPlane, which largely simulates the Gmail experience plus some powerful additions, the Sparrow client is designed to be minimalist.
As John Gruber (Daring Fireball) points out, the design for this Gmail client seems to be inspired by Tweetie for Mac. The developers Dinh Viêt Hoà and Dominique Leca ignore the traditional email client stereotype and aim for simplicity in a way that is rather inspired. Sparrow has “just your mail, and nothing else.”
Sparrow currently supports message threading as well as using multiple accounts. In the future, you will be able to use other IMAP email accounts (such as MobileMe) as well as gain the ability to use Gmail labels. It is free and available now, so check out the beta and let us know your thoughts.”