Some open-source projects provide mirrors on GitHub.com in addition to their official repositories, which are hosted elsewhere.
Here are a few prominent repositories that are mirrored on GitHub.com:
- The Apache Software Foundation
- The Chromium Project
- The Eclipse Foundation
- The FreeBSD Project
- The Glasgow Haskell Compiler
- The Linux kernel source tree
To set up your own mirror, you can configure a post-receive hook on your official project repository to automatically push commits to a mirror repository on GitHub.com (or GitHub Enterprise).