To be more precise, we support the entire "modern" function library in excel, that can be implemented without dependencies on Microsoft products/services. So if it can run locally, and isn't platform dependent, we run it. We, for example, support https://support.microsoft.com/en-us/excel/functions/filterxm... , so in some ways, we support more of excel than excel on non-windows platforms :P

We also support what-if scenarios, arrays, spills, cycles, all the non-cloud / non-DLL excel functions, data tables, conditional formatting, charts (though we don't allow creating / editing at the moment, that's coming very soon, there's a lot of configuration surface in those things, and we want the experience to be really good), etc. If you haven't tried it, maybe take it for a spin, I think you'll be pleasantly surprised with how much functionality we have.

Our biggest deficiency right now (in my opinion) is pivot tables, we don't let you create / edit / recalc them (though you can still build formulas on them). Our engine supports them, but we're still doing a bunch of testing on it to make sure it's rock solid before we turn them on for people.