The MIT project that produced Macsyma ran from about 1967 to 1982 or so. It was sponsored at various times by ARPA, NASA, DOE, various industrial contributors. The people in charge of the project sold an "exclusive" license to commercialize it to Symbolics, Inc. The rights were eventually sold to Macsyma, Inc, where it seems to have stopped. Maxima is a clone of Macsyma released under the GNU public license.

In order to download Maxima, please click the link below. 

http://sourceforge.net/projects/maxima