Question in question: How to keep open source projects up to date
This question is asking for software recommendations that is commonly utilized for version control (though doesn't mention "version control" by name).
Is this type of question on topic here?
I don't think the question is asking for recommendations of VCS. Instead, it is asking for knowledge about the existence of VCS: the OP has a problem about collaboration, which he wishes to solve with a program. VCS is likely not the only way to do this, so other answers may be valid as well.
However, that does fit into the category of Idea Generation (which is not a close reason we have here, but other sites do). Idea generation questions are banned on other sites because there is no objective way of judging which answer is the best: one recommendation is as equally valid as another.
In my (strong) opinion, no. If we allow these types of questions, we'll get license-recommendation questions... Noting this message in chat, those will (sorry, but they will) lead to endless debates and arguments about which license is better than another, which is not something we want to have to clear up.
No. I do not think this type of question is on topic. This question doesn't have anything to do with open source (other than the VCS options are open source).
If "open source" was removed from the title, the answers would remain the same (use version control).
Shopping: no. Recommendations: yes. Most questions that ask for some kind of recommendation are not shopping questions.
Inasmuch as software that's specifically relevant in an open source context is on-topic here, recommendations for such software is on-topic. The Software Recommendations site has established guidelines for good software recommendation questions as well as answers. I encourage recommendations for software that's specifically useful to a particular community to be asked on a site where the audience is that community, rather than on SR.SE. SR.SE does ok with generalist software, but lacks community expertise when it comes to questions that require experience in a specific domain.
How to keep open source projects up to date is basically looking for the answer “use version control”. It isn't a shopping question. It isn't even a recommendation question. It's a question about methodology. I fail to see what makes it off-topic.
