Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is modeled after Mozilla Firefox. It supports POP (storing mail locally on your hard drive so that it can be accessed without an internet connection), and IMAP. It features excellent mail filter capabilities and management. Thunderbird has strong support for using multiple accounts and identities, including automated signature features.
- Cannot handle google calendar by default (needs plugins). Same for contacts etc.