GitHub is a source code repository service based on the popular git software written by Linux-creator Linus Torvalds. It is operated by a San Francisco-based American Microsoft-subsidiary which was started as an independent company in 2007 . It is used by a lot of free software projects. It is a huge single point of failure for the free software movement.
Hosting a software project on GitHub is free and there are built-in economic incentives to do so. There's also plans for "professional" and "enterprise" accounts.
GitHub.com was an OK site for years, but then Microsoft bought it for $7.5 billion in 2018 and things went downhill fast. MS has since brought tons of anti-features and gets in the way of developers every step of the way. One such obnoxious MS practice is to get on everybody's nerves with passwords. What passwords any user chooses is none of MS'es business, yet they disallow access of the developers to their own work, until they jump through MSes password hoop. This is just one example of the hostile stance that MS is taking against developers.
The Rise Of Censorship
Github used to allow all kinds of emulation software to exist on their platform. This changed immediately after Microsoft bought Github. Microsoft will remove emulators from github  if someone asks them to do so.
Github launched a "sponsors" feature in May 2019 which gives free software projects a tangible inventive to host their source code repositories there. Github-users can use this feature to donate/pay Github-projects they like. This is why some more laughable free software "forks" like the GIMP-rebrand Glimpse use GitHub to peddle their ripoffs.
- Nintendo Asks GitHub to Shut Down Game Boy Emulator, July 23 2018