Apache OpenOffice Community Forum

Just stumbled across this 'The Register' article. Seems people are actively working on the capacity for multiple people to work on the same LibreOffice document in real-time. Interesting stuff, though I suspect it will take a fair amount of time to get out of beta.

LibreOffice still kicking at 40, now with browser tricks and real-time collab

MS Office used to do that even before MS365. It's more a OneDrive thing I think.
The trick is rather in the management of the changes. The only difference being that each time an operation is done, it needs to be sent to the code managing the save operation so that it is immediately saved and then refreshed on the other instances that are open.