MailStore - MailStore Home - A 100% free single-private-user desktop solution
imapsync - Console-based utility for migrating IMAP mailboxes.
Yippie Move - The world's best email transfer tool
OfflineIMAP - OfflineImap synchronizes email between an IMAP server and a MailDir or between two IMAP servers.
Fetchmail - The Fetchmail Project
Gmvault - Backup the emails in your Gmail account.