MailStore - MailStore Home - A 100% free single-private-user desktop solution
imapsync - Console-based utility for migrating IMAP mailboxes.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
Gmvault - Backup the emails in your Gmail account.
Fetchmail - The Fetchmail Project
Loop Email - Emailing for teams: Organize your Inbox into channels 💌