I recently made a little tool for pinging the GitHub API, getting a list of all the repos the user owns or has starred, then downloading them locally. It's on GitHub if anyone would like to try it out.
I typically have this set up as a cron job to run every day or two so when I'm not going to have internet access for a couple days I can still keep doing things.
https://github.com/Michael-F-Bryan/github-backup
If you give it a shot, let me know how you go and if you think it's worth putting up on crates.io so others can cargo install it.