I used to love playing with scientific calculators when I was a kid because they seemed so other worldly and powerful. Nowadays, mobile phones have more technology in them than scientific calculators.
However, for those of you that use a calculator for something more than basic math, Free42 is a powerful scientific calculator for all but the most highly complex scientific calculations. Free42 simulates the HP-42S scientific calculator and is a completely free, open source project.
Free42 can be used for everything from simple mathematical equations on statistical calculations to probability calculations. You can even view results in a multidimensional format. The amount of platforms that Free42 supports is impressive, including iPhone and iPod touch, Windows, Pocket PC, PalmOS, Mac OS X (available as an application and Dashboard widget) and Linux (x86). The dashboard widget is a particularly useful replacement for the rather limited one that comes with OS X.
Free42 is not exactly the kind of calculator you need for adding up your shopping bill but for those who need a serious scientific caluculator, it's everything you need and more.