Application that solves math expressions. Main features:

Supports variables (e.g. you can do "a=5", then "a+1" and you get 6)

Built-in basic function (like logarithms and trigonometry)

Custom functions can be defined (e.g. "log(x,b)=log(x)/log(b)", then log(32,2) will print 5)

Variables and functions can be edited both from the prompt and dialogs

Can print parsing and evaluation steps.

(Android 6.0+ only) can evaluate expressions from text selection in any application