Mathematica is a computational programming tool used in science, maths, computing and engineering first released in 1988. It is proprietary software that you can use for free on the Raspberry Pi and has been bundled with Raspbian and NOOBS since late 2013. Read the announcement on the Raspberry Pi blog: The Wolfram Language and Mathematica on Raspberry Pi, for free.

See the Getting Started with Mathematica learning resource for instructions on using Mathematica.