Jupyter - Project Jupyter exists to develop open-source software, open-standards, and services for interactive computing across dozens of programming languages. Ready to get started? Try it in your browser Install the Notebook.
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
iPython - iPython provides a rich toolkit to help you make the most out of using Python interactively.
Giac/Xcas - Free computer algebra system
Kajero - Interactive JavaScript notebooks - create good-looking, responsive, interactive documents.
Geometry Pad - Geometry Pad is a dynamic geometry application for iPad and Android tablets.