GitLab is decent, with an open source core that can be installed on premise — I introduced it for a former employer and they are still very happy with it.
All isn't perfect and I'm still on GitHub due to the network effects, but you do have alternatives.
Since the news broke I've been hosting a Gitea instance and while that works fine, I cannot go a day without using Github for things like pulling other people's code, creating issues, etc.
Seriously it only takes a bunch of high profile projects and people to drive a migration.
In other words Microsoft has to play nice.
SourceForge is from before my time. When Github was still small, I was still being brainwashed by school's free Windows and discount Office licenses and school educating us in using Microsoft Office. From my current point of view, though, SourceForge was never as big as Github is now. Almost every development company pulls code from Github, either in an automated fashion to pull in updates, or casually as they need random things that are published there. I don't think that was ever the case with SF.
If you have more feedback on the things that could be better, we would love to hear more!