The CBAM system gives you the ability to create asynchronous multiplayer games with server based savegame storage. If you don't know what asynchronous multiplayer means, take a look at the FAQ.
To use CBAM you need - beside the RPG Maker MV of...
Oof, this "side project" of mine is starting to get as complex as a VS plugin, at least as far as plugin parameters are concerned. I think I now understand why a plugin like this doesn't already exist(that I know of). Learning a lot while trying to make it work though!