Wolfram on Pi

Online ebook on Mathematica
http://www.wolfram.com/language/elementary-introduction/
which comes in Kindle, .nb,

Also, an online app allows you to use Mathematica in the cloud at many fee levels, including FREE!
https://lab.open.wolframcloud.com/app/

even more wonderful, the raspberry pi has a free "home use license" for Mathematica as part of the standard raspbian image (currently "jessie")
Raspberry Pi

A full version of the Wolfram Language is available for the Raspberry Pi computer and comes bundled with the Raspbian operating system. Programs can be run from a Pi command line or as a background process, as well as through a notebook interface on the Pi or on a remote computer. On the Pi, the Wolfram Language supports direct programmatic access to standard Pi ports and devices.

Imagine a number of Mathematica programs on separate but network connected raspberry pi's !

Note there is a description of setting up a weather station on a pi, using Mathematica as the controlling computer.