I know Liveblocks.io has been making this very easy and accessible over the last few years. They recently introduced AI, and are promoting that of course, but as I understand it multiplayer collaboration (https://liveblocks.io/multiplayer-editing) is their meat and potatoes.
Not affiliated with Liveblocks, just aware of its existence.
I work at Liveblocks—yes! Our founders were inspired by Figma and wanted to make it possible for others to build apps like this more easily. We provide our own sync engine, Storage, which is aimed at this use case.
ctnicholas|6 months ago