collaborative map software?

Avenza seems to be the go-to app. It works pretty well and all, but I'm wanting to know if there's any software available that can allow a team of people to simultaneously access and make edits/notes to a geo-referenced map. It also need to have kind of the same base functionality of being able to show your current location and all that. Ideally it should be designed for mobile first, but being able to access it from desktop too would be a plus.

So, just for one example, I could add a placemarker on the map, and any of my team members who are also accessing that map will be able to see (in real time) the placemarker that I just made. Does this type of feature exist?