It is a spreadsheet online that anyone can edit together. It uses excel syntax for formulas. I haven’t really pushed it too much, but it handled what little I gave it. You can import your stuff for a collaborative session and then export it when you are done. I know Sam and I will probably use this when we are looking at the numbers on our house. Pay attention to the warning on the page though, there is no security on this app – don’t put anything up there that you want to keep secret.