I'm a huge fan of draw.io - a tool used to draw network topology, UML, architecture & more. Our team uses the tool pretty heavily, albeit independent to each other and not necessarily sharing.
I had a thought.. you have the ability to export as .xml. Each user edits their diagram, exports as .xml (to device) and adds to the SCM repository. If another user wants to edit it, they check-out the branch.. make their edits and check in/add a pull request/etc.
draw.io + SCM = success?
Has anyone else used this type of combination?