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In my opinion Github in its current incarnation mainly exists to steal the IP of programmers and lock it up in proprietary AI services controlled by Microsoft. It dominates for the same reason Facebook or Youtube dominate. It is the only platform normies know and it benefits from massive network effects. It is US owned and operated which is becoming an issue for lots of people. Github is a proprietary closed source platform. I believe it was originally mostly written in Ruby but they have likely replaced all the performance bottlenecks using other languages. In my opinion their site is a usability nightmare.
Forejo is a fork of Gitea by Codeberg, a community run non-profit from Germany (still a liberal democracy under the rule of law) and hosted in Europe. They provide free hosting for open source projects or it is easy to self host. Gitea is a fork of Gogs and remains active. All those forks are written in the Go language and it requires a single exe, a config file and an sql database to run making it very easy to self host even without containers.
Gitlab is a service like Github or Codeberg that can also be self hosted but it is written in Ruby, a slow and inefficient interpreted language, which like Javascript or Python has lots of crazy fragile run time dependencies. The open source project was originally a work of Dutch and Ukrainian programmers and it was a Dutch company but they took VC money and IPOed and I don’t know that I would assume it is European controlled. Some open source projects like Gnome moved there as it was the main alternative to Github. Can’t recommend vs Gitea/Foejo for self hosting.
For single developers, small groups, arguably all you really need is git and email if you don’t need or want all the extra fluff. That can work even for large projects like the Linux kernel. Sites like github tend to serve as single points of contact for lots of projects. It is their front page, issue tracker, everything which is one hell of a dependency on another company. It has Facebook-ized the code ecosystem. I think it also sort of serves as a linkedn for some people.
It isn’t relevant to the Linux kernel at all. Even though Torvalds wrote git to support Linux development they operate on a different development model (email, patch sets etc). It is very relevant to the wider ecosystem (Linux distro vs Linux kernel). Most open source software development is hosted on one of these platforms and even non-developers sometimes need to interact with them. Anyone starting a project or looking to share it finds themselves asking the same questions.
I prefer this sort of engagement farming question to the ones asking which laptop to buy or which distro or desktop environment is best. Though it is arguably healthier and more productive for me to be doing almost anything else with my life. I increasingly feel like I am filling out a captcha every time I answer such a question. It feels like something any reasonably competent human could discover trivially hitting a small number of websites and reading. Even the people who cut and pasted low effort LLM responses pretty much nailed most of the facts - arguably more than good enough. What is the point of participating here really?