http://macmost.com/ In your Mac's Applications folder you've got a Calculator app that you probably haven't given a second look. This is much more than a simple utility. You can use it in scientific and programmer mode, convert units, time and currency, work in octal and hexadecimal, produce a tape of your calculations, and even get it to talk to you.
Whether you use your Macs for personal or business use, chances are you aren't using them enough. Use them more! Use them for everything! Rule the world!