What can't you do in Excel?
jblondon: 1. It should be possible to turn a sheet into a function. So I can then define my own 'inputs' and 'outputs' for that sheet, and 'call' it with whatever parameters I like from another sheet. Sure it can be done in code, but for building large, maintainable models that's not practical.2. 'Hard' and 'Soft' numbers (i.e., numbers I manually enter vs. numbers that are the result of a formulae) should be automatically coloured accordingly if I want them to be. Manually plugging in a number on top of a formula should not necessarily over-write the formula. It's quite common I want to preserve the logic but 'hack in' a variable. Instead, it's either or (and I have to copy/paste the formula into a comment for the cell, which is a pain and clumsy as hell).3. Track changes.4. Non-euclidean topology ... by which I mean, making it possible to vary the number of colums / rows and column / row sizes within a single sheet.