Firefox - Thunderbird

Mozilla Thunderbird is a free, open source, cross platform email and news client developed by the Mozilla Foundation. The project strategy is modeled after Mozilla Firefox, a project aimed at creating a web browser. On December 7, 2004, version 1.0 was released, and received over 500,000 downloads in its first three days of release (and 1,000,000 in 10 days). As of 2008, Thunderbird has been downloaded more than 60 million times since 1.0 release.