It'd be interesting to see how much a multi-country effort to make a tool that collects tax information and applies a set of rules to the data to advise the user would be able to share. My impression is that it'd be a lot (the rules, of course, would be specific to the type of entity and local legislation).

As a Brazilian who has been using free government-provided tools to submit my taxes for decades (up to when I moved to Ireland, where I don't even need to do that), this is very interesting to me.