Smart Math Calculator is a convenient calculator that has over 20 math functions and scientific constants which you can type and see the results.
This tool helps you to have multiple expressions at same time and also assign their result to variables and then use the variables in other expressions, creating your own functions that receive one or more parameters.
I like its simple interface and the ability to print the results. It it rather functional and precise. I tested it on some math problems from high school, and it worked well. Though it took me some time to get used to its full functionality.