SMath Studio is a tiny, powerful, free mathematical program with
WYSIWYG editor and complete units of measurements support.

It provides numerous computing features and rich user interface
translated into about 40 different languages. The application also
contains an integrated mathematical reference book.

It can be easily extended based on your needs. A built-in Extensions
Manager tool allows to get access to hundreds official and third-party
resources of the following types: usage examples, plug-ins, SMath
Viewer based applications, snippets, interface translations,
interactive books, handbooks and tutorials.