Forgejo was soft forked from Gitea after they went commercial and changed the license (I think). If there aren't any so far, expect pay walled features eventually.
Forgejo turned into a hard fork after communication issues between the teams. I haven't looked too deeply into it (as I don't really care about the fact that it's a hard fork now). This means while it used to be a drop-in replacement allowing you to go back and forth between the two, it's now an active conversion, I think.