Windows Calculator provides you with a powerful but simple calculator.
Windows Calculator features standard, scientific, and programmer modes, and also includes a unit converter allowing you to utilize Windows Calculator for almost anything. From adding up a bill, converting measurements, or even completing complex math problems like algebra or geometry, for instance - it's all there. It also includes Calculator history so you can go back and check your input numbers are correct.
Windows Calculator is displayed from a streamlined interface so you can concentrate on the computations rather than operating an overly-complex app. And it can be open in multiple windows at once, allowing for multitasking.
Free42 HP-42S Calculator Simulator is an Open Source recreation of the HP-42S Scientific Programmable Calculator and HP-82240 Printer. Plus42 is also available.