imapsync - Console-based utility for migrating IMAP mailboxes.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
MigrationWiz - MigrationWiz provides on-demand mailbox migration services through a fully automated cloud-based...
Gmvault - Backup the emails in your Gmail account.
Mail Backup X - Your one stop mail backup and archiving tool for Mac.
Fetchmail - The Fetchmail Project