I work on an open source project for doing just that: https://plane.dev https://plane.dev It follows the model used by Figma where each active document gets it

I work on an open source project for doing just that: https://plane.dev https://plane.dev It follows the model used by Figma where each active document gets its own process on a cluster of machines, and requests are routed to the document server. The advantage of this over something like pubsub is that you have a single authoritative server that can persist the document, instead of having to coordinate multiple sources of truth. (We also provide a managed version of Plane at https://jamsocket.com https://jamsocket.com)