I think the “What topics can I ask about here?” help page is quite clear about that:
Questions that you may ask:
…
Running third-party applications on Ubuntu.
This obviously includes git as well as Slack, and this is a good thing IMO. Installing and using e.g. Slack on Windows is quite different from doing the same on Ubuntu, so a platform for Ubuntu-related questions about it is needed. There are certainly questions here which are the same for other systems, but in the majority of cases nobody can be sure this is actually the case – and if it is, it still doesn’t really hurt to have the question on AU. It’s not worth the trouble to filter them out.