MailStore - MailStore Home - A 100% free single-private-user desktop solution
Got Your Back - Got Your Back (GYB) is a command line tool that backs up and restores your Gmail account.
Gmvault - Backup the emails in your Gmail account.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
SysTools Gmail Backup - Backup Gmail Emails, Contacts, Calendar, and Google Drive Storage File by SysTools Gmail Backup Solution
Piler - Piler is an open source email archiving solution with all the necessary features for your enterprise