said by djrobx:
The biggest one is Excel. People use it for so much more than what it is.
Yup. Excel spreadsheets are commonly used as a surrogate UI to a VBA program. Input data in spreadsheet "form" -> Execute VBA script -> Output data with quick access to charting.
I can see why - it's an easy way to distribute sharable software utility programs along with data, without the distribution headaches associated with full blown executable programs.
Excel pivot tables are the bomb, though.