Linux:

Maxima is part of all popular linux distributions, but usually not installed. To install maxima and the graphical user interface wxmaxima, use the graphical package manager of your distribution, or use following shell commands:
Ubuntu:
sudo apt-get install maxima wxmaxima
Debian:
apt-get install maxima wxmaxima

If your Linux system does not contain maxima and wxmaxima, download it from:
maxima: http://maxima.sourceforge.net
wxmaxima: http://andrejv.github.com/wxmaxima

Windows and MacOS:

Download the appropriate version of maxima from
http://andrejv.github.com/wxmaxima
the package also contains both maxima and wxmaxima.

Maxima Tutorials

http://www.math.hawaii.edu/home/wxmaxima.shtml

http://maxima.sourceforge.net/docs/tutorial/en/gaertner-tutorial-revision/Contents.htm

http://arachnoid.com/maxima/index.html

http://maxima.sourceforge.net/docs/manual/en/maxima.html

http://www.csulb.edu/~woollett/