I was mucking about with the spreadsheet at https://cryptpad.fr/ and I'm fairly impressed with that. Again, cryptpad is using OnlyOffice's spreadsheet.
Here's one I'll file under interesting. Not terribly useful in it's current state, but shows promise:
The underlying 'spreadsheet' works fairly well, if and only if you enter data by hand. Copying and pasting from other sources works, but needs some work.
The underlying 'spreadsheet' does/or at least *can* run locally, in a browser without any overhead:
I haven't dug down on the exporting bit to see if it can work locally or not:
https://github.com/SheetJS/sheetjs/tree ... aving-data
The exporting needs A LOT of work.