MailStore - MailStore Home - A 100% free single-private-user desktop solution
imapsync - Console-based utility for migrating IMAP mailboxes.
Gmvault - Backup the emails in your Gmail account.
Mail Backup X - Your one stop mail backup and archiving tool for Mac.
audriga Email and Groupware migration - Easily migrate your email, contacts, calendar items and tasks to your new provider or server. No software installation is required.
OfflineIMAP - OfflineImap synchronizes email between an IMAP server and a MailDir or between two IMAP servers.