GYB
Got Your Back (GYB) is a command line tool for backing up your Gmail messages to your local computer. It uses Gmail's API over HTTPS.
Downloads
You can download the current GYB release from the GitHub Releases page.
Documentation
The GYB documentation is hosted in the GitHub Wiki
Mailing List / Discussion group
The GYB mailing list / discussion group is hosted on Google Groups. You can join the list and interact via email, or just post from the web itself.
Author
GYB is maintained by Jay Lee. Please direct "how do I?" questions to the mailing list.