I made the following script to download all Github projects into a directory. It is fun to see everything you have accumulated over the years. :)
curl -u <USERNAME>:<OAUTH_TOKEN> https://api.github.com/user/repos\?per_page\=100 | jq ".[].git_url" | tr -d '"' | while read in; do git clone $in; done
<USERNAME> is your github username.
<OAUTH_TOKEN> can be created from here. You only need the repo scope for this.
You may need to install jq as it isn't standard.
You will need to be authenticated or the git clone X will fail on non public repos.
API will only download up to 100 projects. If you have more than that you will have to page.