I think you'd find some fascinating answers on accounting, finance and actuarial forums, that might not turn up on HN.

A few years ago I worked on a couple of different financial services projects that involved porting massive Excel-based jobs over to sturdier setups. Even the relatively simple spreadsheets (for people with a finance background) were long, complex projects that needed an RDBMS, an R or Python program, and a web app to do what Excel was just about handling on its own.