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.
Linux / MacOS
Open a terminal and run:
bash <(curl -s -S -L https://git.io/gyb-install)
this will download GYB, install it and start setup.
Download the MSI Installer from the GitHub Releases page. Install the MSI and you'll be prompted to setup GYB.
You can download the current GYB release from the GitHub Releases page.
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.