Live shared spreadsheet

I would like to implement a server to allow multiple users to work with the same spreadsheet and see each other's updates in real time, a la Google Sheets.  (My current system uses Google Sheets, but for the 3rd time in 3 years Google has made a change that breaks my work, this time with no solution besides going to each sheet [of thousands] and making manual edits, so I'm done with building on that platform.)

I'm just getting up to speed on the Vaadin spreadsheet add-on, and at this point I don't see an obvious path.  I don't see anything like a data source object that could be shared around -- have I missed that?  At any rate, I'm looking for any advice (or other options, also).

Thanks,
Bill