n01getsout

Qalculate is perhaps the most advanced calculator I have ever seen. It has separate GTK and QT interfaces, so it will integrate well with whichever desktop you use. It may take you a while to figure out how to do what you want, but be assured that it will do what you want. Qalculate can solve most equations and inequalities, has several hundred built-in functions, has a RPN mode, shows if the result is approximate or exact, and keeps a history of calculations.