Viewer of Excel spreadsheets for people who don't run or want to run Office.

This app is awesome, and brings new meaning to old school — they have Mac System 7 versions still available and supported, y'all.

What I like is that unlike everything else (including MS Office itself), it presents it as the original sender was trying to present. It's also a very small memory load and is extremely light-weight, which makes loading an Excel spreadsheet just to double-check something far less of a chore than it can otherwise be.