Numbers is a really useful spreadsheet program that comes in the Apple iWork suite. I'm a big fan (I wrote the official book after all). I just stumbled across this great website called NumbersTemplates.com that offers a ton of free templates that makes Numbers even more useful.
Some of my favorites include.
Project Management Template
Baseball Scorecard
Scuba Log
If you are on the fence, don't be. The application suite costs $79, has a 16% market share, and reads and writes all of the Office Formats.