There’s plenty of “scientific calculator” programs around, but very few really live up to the name (trig functions and a degrees/ radians switch really aren’t as advanced as some developers seem to think).
At first glance the Windows freeware Sicyon looks much the same. There’s a numeric keypad, the basic operators, then buttons of functions which you can use as required.
Check out the menus and toolbars, though, and you’ll find modules to fit curves, find minimums/ maximums/ integrals, derivatives and roots, generate graphs, convert units and more.
There are also databases of values covering various physical and chemical properties and topics: physical constants of gases, liquids and metals, speed of sound in different media, conductivity of various material, density of water/ mercury/ air at different temperatures, the Periodic Table and more.
If this isn’t enough, you can create and access VBScript or JScript functions from the calculator, even run program code on demand from the main window.
Sicyon’s interface is a little quirky, and you should expect to spend a while playing around before you understand how it works. But if you need a scientific calculator which actually deserves that name then going to be worth your time.