Overall it's very disappointing that Github didn't decide to embed issue tracking (and also PR discussions) inside the repository (in another branch perhaps). Issue discussion is part of documentation IMO, and not distributing it alongside the repository causes lock-in
https://github.com/MichaelMure/git-bug
https://github.com/dspinellis/git-issue
https://sciit.gitlab.io/sciit/ (this one has a list of alternatives here https://sciit.gitlab.io/sciit/#other-distributed-issue-track...)
Overall it's very disappointing that Github didn't decide to embed issue tracking (and also PR discussions) inside the repository (in another branch perhaps). Issue discussion is part of documentation IMO, and not distributing it alongside the repository causes lock-in