We wanted to have a "common" subsystem that was common across projects. Being able to add and work on the common area and new projects at the same time was important. Pushing the common area back and being able to deploy to the older projects and test was important.

This seems difficult in git.

There are "submodules" and "subtrees" but none seemed particularly great and as far as I could tell each came with a bunch of caveats.

I'll admit my Git skills aren't great, but I've used a variety of source control and tried to suss out the best way to deal with a small team.

We ended up using "git subrepo" which is an add on thing I don't love, but it works.

part of the motivation is "common" and "project 2" are to be open sourced, but "project 1" which also uses "common" isn't.