You can turn Excel spreadsheets into web applications quite easily with Google Apps Script. We wrote a REST interface to a massive multi tab Excel file recently

You can turn Excel spreadsheets into web applications quite easily with Google Apps Script. We wrote a REST interface to a massive multi tab Excel file recently and it only took like an hour, as opposed to days of reverse engineering the calculations (the client did not know what the equations in the file were because the employee who created it left). Basically I'm saying it will get much, much worse before it gets better.