Groups for sites

I have a server that hosts lots of Statamic sites for different clients. I would love to group those sites by client. I thought that I could use projects for this. However, the problem with this approach is that you can only assign a server to one project. It would be great if you could assign a server (maybe even sites) to multiple projects.

Or maybe projects are the wrong approach and a new tagging feature would make more sense. I basically wish for a better overview when scanning the sites panel. Groups seem to give me that.