PrintGitHub is a great fit for managing open source code projects since, with a free account, all repositories are available on the internet at large. For example, the open source GIS software QGIS (see Lesson 4) is housed on GitHub at GitHub's qgis/QGIS page. Take a look at the repository.
On the front page, you can see in the dashboard statistics that (at the time of this writing) there have been over 40,000 commits, 50 branches, 100 releases, and 250 contributors to the QGIS project. Users worldwide can now contribute their ideas, bugs, and code improvements to a central location that can be managed with standard version control workflows.
Some software companies that have traditionally been protective about their code have adopted GitHub to open certain projects. Esri is rather active on GitHub at GitHub's Esri page including the documentation and samples for the ArcGIS API for Python (see Lesson 3). Microsoft also is present at the GitHub Microsoft page with the tagline “Open source, from Microsoft with love.”