SpeedCrunch is a portable keyboard-based scientific calculator.
The program is built for extreme ease-of-use. Type expressions, press Enter, the results appear in the history window: simple.
SpeedCrunch isn't strict about syntax. It doesn't care whether you enter 2+2 or 2+2= , you still get the same answer. And if that isn't quite what you meant, no problem, double-click "2+2" in the history window to recall that line, and change it to whatever you like.
There are 80+ mathematical functions to explore, but these are also easier to use than you might expect. Start to type a function name and autocomplete displays possible options. For example, typing A gets you abs, absdev, ampere, and, angstrom, ans, arccos, arcosh (the expanded name is displayed after each one to help you identify it). Click whatever you need and it's entered for you.
SpeedCrunch does its best to help with your expressions, too. A built-in Formula Book has simple prebuilt items you can enter with a double-click (quadratic equations, volume of a cone, area of a cylinder), or you can insert more than 150 scientific constants with a click or two.
All your calculations can be carried out with up to 50 digits of precision, with support for complex numbers, base and unit conversions, and more.
You can change most of this even after you've entered your data. Select Settings > Result Format > Binary, for instance, and the result of 2+2 becomes 0b100.
Individual sessions may be saved, allowing you to carry on later, or you're able to export them as plain text or HTML.
An excellent calculator with a lengthy list of powerful features, but is still easy enough for math novices to use.