Verified Link

GitHubGitHub

GitHub Usage Statistics · Download List of All Websites using GitHub

The website mentions github.com in some form.

Web Servers

ApacheApache

Apache Usage Statistics · Download List of All Websites using Apache

Apache has been the most popular web server on the Internet since April 1996.

Operating Systems and Servers

UnixUnix

Unix Usage Statistics · Download List of All Websites using Unix

A *nix based operating system (undisclosed).