fxCalc is actually one of the most advanced desktop calculators for Windows. The biggest advantage is the simple and intuitive handling of complex mathematical tasks. Starting with a familiar calculator window, it allows calculating self defined functions, sums and products. It takes for instance just a few clicks to run the Leibnitz iteration to calculate Pi. fxCalc lets you define, analyse, visualise and calculate scientific functions and is a full featured replacement and/or enhancement of the old fashioned Windows calculator. In addition to calculation and visualization you can analyze and solve scientific functions and perform linear regression. Even if the Window concept may not look advanced, it provides the big advantage of opening similar windows multiple times to compare the results as needed. To use the interpreter DLL in your own projects, you can obtain a copy and documentation of this DLL directly from the author. 

Key features:

Windows
Installer XP/Vista/Win7/Win8/Windows 10 32 & 64 bit version (pay attention to dependencies !) 
fxcsetup_en.exe Version 4.8.4.0 Release Notes 16.06.2016 1.7 MByte 
DotNetfx Version 4.0  Download 