frink - is a practical calculating tool and programming language designed to help us all to better understand the world around us, to help us get calculations right without getting bogged down in the mechanics, and to make a tool that's really useful in the real world. It tracks units of measure (feet, meters, kilograms, watts, etc.) through all calculations, allowing you to make physical calculations easily, to mix units of measure transparently, and ensures that the answers come out right.
That's really cool, and when I was studying chemistry and physical chemistry, I found that the best way to make sure you were on the right path was to keep track of the units, make sure the units work out, and then focus on the numbers. It looks like this is what this tool does as well.