Sparrow is an email client for Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

. After a 4 month beta period Sparrow went on sale in the Mac App Store

Mac App Store

The Mac App Store is a digital distribution platform for Mac OS X applications developed by Apple Inc.. The platform was announced on October 20, 2010 at Apple's "Back to the Mac" event. Apple began accepting app submissions from registered developers on November 3, 2010 in preparation for its launch...

 on 9 February 2011 and it has become the top paid and top grossing app in less than one day.

Sparrow's hallmark is a simplified user interface

User interface

The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...

 reminiscent of Twitter

Twitter

Twitter is an online social networking and microblogging service that enables its users to send and read text-based posts of up to 140 characters, informally known as "tweets".Twitter was created in March 2006 by Jack Dorsey and launched that July...

 clients such as Tweetie

Tweetie

Twitter is a client for Twitter, the social networking website. There is a mobile version that runs on iPhone, iPod touch, and iPad, and a desktop version runs on Mac OS X Leopard and Snow Leopard ....

 or iOS apps, as opposed to a more traditional email style such as Apple's Mail

Mail (application)

Mail is an email program included with Apple Inc.'s Mac OS X operating system. Originally developed by NeXT as NeXTMail, a part of their NeXTSTEP operating system, it was adapted, following Apple's acquisition of NeXT, to become OS X's Mail application.Mail uses the SMTP, POP3, and IMAP protocols,...

 or Mozilla Thunderbird

Mozilla Thunderbird

Mozilla Thunderbird is a free, open source, cross-platform e-mail and news client developed by the Mozilla Foundation. The project strategy is modeled after Mozilla Firefox, a project aimed at creating a web browser...

. Sparrow currently works with Gmail

Gmail

Gmail is a free, advertising-supported email service provided by Google. Users may access Gmail as secure webmail, as well via POP3 or IMAP protocols. Gmail was launched as an invitation-only beta release on April 1, 2004 and it became available to the general public on February 7, 2007, though...

 and Google Apps

Google Apps

Google Apps is a service from Google providing independently customizable versions of several Google products under a custom domain name. It features several Web applications with similar functionality to traditional office suites, including: Gmail, Google Groups, Google Calendar, Talk, Docs and...

 accounts via IMAP, along with IMAP email accounts. It also includes features such as drag-and-drop

Drag-and-drop

In computer graphical user interfaces, drag-and-drop is the action of selecting a virtual object by "grabbing" it and dragging it to a different location or onto another virtual object...

 attachments, Growl support, Gmail labels, and keyboard shortcuts, as well as threaded replies and easy switching between accounts.