Unless you want those people to have merging rights, collaboration can be easily done with exporting a read-only version of the git repo via http (even a browsa

Unless you want those people to have merging rights, collaboration can be easily done with exporting a read-only version of the git repo via http (even a browsable one using cgit). Then anyone can work on their copy, generate patches (git format-patch) and send the files via any means of communication (email, slack,...).