While there was of course great variety... the most common would have been an email mailing list.

Maintainers of a piece of software would run some kind of VC repository usually, although not usually a distributed one like GIT - they were networked. Some people had commit access. You'd keep a changelog, just like today, and the group would tag and release, just like today.

What Git/Github brings to the table is really the combination of a distributed version-control system that gained large traction (GIT) and a system to leverage that to make common collaboration tasks easier (fork, pull request, tracking meta-data, etc).