MailStore - MailStore Home - A 100% free single-private-user desktop solution
imapsync - Console-based utility for migrating IMAP mailboxes.
Got Your Back - Got Your Back (GYB) is a command line tool that backs up and restores your Gmail account.
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.
Gmvault - Backup the emails in your Gmail account.
OfflineIMAP - OfflineImap synchronizes email between an IMAP server and a MailDir or between two IMAP servers.