Serverless Solution Design: Distributed Multi User Browser Session Synchronization

Assume a browser based (or desktop electron) stand alone, client side only application. Multiple users are working with that application at the same time, on their own laptops and at (possibly very) different locations, possibly across the globe. It is conceivable that they are working on a common object. A document, diagram, gameboard, technology radar, whiteboard etc. If that is the case, it would be useful if not necessary for the content to be synchronized across the browser environments.