SpeedCrunch is an Open Source, cross-platform scientific calculator that features a fast, keyboard-driven user interface with some useful features.
It comes ready to perform with a built-in formula book which is great for reviewing and inserting commonly used formulas, such as the volume of a cone for instance. You are also able to define your own functions if you need more than the default 80 that come pre-loaded.
SpeedCrunch will keep track of all your work within a scrollable history if you need to double check a piece of your calculations for accuracy it is all there. Additionally, you can use the customizable syntax highlighting option that will provide an easy way to spot mistakes.