Github just needs to rethink how tagging all users works and a way to prevent this.
It’s different from “source available” - open source should let you fork and reuse it.
For example there is microsoft shared code license, that’s “here is the code, but copyright is still ours, you can’t do anything with it but look”.
I have no idea what kind of license (if any) is unreal engine.
If you write your own licence (not recommended, but some developers and especially corporations do) it could be even fully compliant, but not approved.
Both of them are pretty poor descriptors. "open source" doesn't convey the legal freedom you are granted (as you have just found out), and "free software" makes it sound like it's just about price.
If someone lets you see source code but doesn't allow you to do anything with that code it's not what people would call "open source", you could probably call it source-available or something. "open source" has a specific legal definition that means code released with a permissive license.
open source implies the right to redistribute source code.
Edit: I doubt the license for this code is an OSI-approved one with this registration business. But I have not checked and I won't check.
I think this is the closest you can come to a "formal definition", short of a law defining the term.
OSI in fact tried to file for a trademark on 'Open Source' in 1999 [1], but failed because the term is 'too descriptive'.
[1] https://opensource.org/pressreleases/certified-open-source.p...
The idea is that nobody is going to get a million dollars in revenue from a game without being visible enough that Epic's receivables department can bill you. So they can ignore the 99.99% who download it and never get a hit.
I'm amazed that 400,000 people have downloaded Unreal Engine, though. It's really complicated, hard to use, takes hours to compile, and is only worth the trouble if you're making an elaborate 3D game. Not that many people do that.
I suspect the "real" reason for the current rigamarole is to get your details for their marketing team.
https://docs.unrealengine.com/4.27/en-US/SharingAndReleasing...