SMath Studio is a small but powerful, free mathematical program with a WYSIWYG editor, which provides numerous computing features and a rich user interface translated into 40 different languages.
It provides you with a paper-like interface for performing your computations, and it can be tweaked a little to suit your preferences by changing font size, functions style, text color, background color, and arguments separator, to name a few. You can also fine-tune the calculations depending on what you are working on.
SMath was designed to be a free version of PTC Mathcad. It can solve differential equations, graphing functions in two or three dimensions, symbolic calculations including solving systems of equations, matrix operations including determinants, find roots of polynomials and functions, symbolic and numeric differentiation of functions, numeric integration, simple multiline looped programs, user-defined functions, and units of measurement.
You can also extend SMath with the built-in Extensions Manager tool, which allows you to get access to hundreds of official and third-party usage examples, plug-ins, SMath Viewer-based applications, snippets, interface translations, interactive books, handbooks, and tutorials.
SMath is a strong competitor to Mathcad, considering that it's free. Donations are accepted