Excel is the spreadsheet application included in the Microsoft Office suite of programs (which includes Word, PowerPoint, and other applications. It was originally released for Mac in 1985 and for Windows in 1987.
Google Docs is comparable to Microsoft Office – except that it is an online application. Docs has applications for documents, spreadsheets, presentations, drawings, and forms. Google Spreadsheet is not quite as full-featured as a software-based application, but still has a large collection of functions and basic charting capabilities. By the way, did I mention that it is FREE?