I've been looking for a planning tool for a small team for some time. I haven't even tried this, but I just love the fact that a game developer wrote this over 14 months because of a vacuum of planning tools that aren't cloud-oriented enterprise SaaS. It's not open source, but you can build it for your own use and it runs entirely offline, with its datastore in plain text (JSON) so it can be version controlled. This is completely up my alley! If you're interested in a pre-compiled binary, the author has made releases available on itch.io for $15. Very cool!

GitHub - SolarLune/masterplan: MasterPlan is a project management software