Forgejo, Gitea

Those are using forks of nekos/act, while Forgejo act is fork of fork.

e.g. gitea use the act_runner binary to run locally it has a command for that

Side note: use .github/workflows on Gitea if you don't use Gitea Actions Extension (yes there are multiple differences to allowed syntax)

Gitlab, Radicle

I don't think this is a good idea, at least gitlab pipelines are fundermentally different