Sales of the book don't matter to Wolfam -- Mathematica is MUCH more lucrative. The book is just an advert for his software.

Believe it or not there are open source computer algebra systems! Two that I'm familiar with are Maxima and PARI-GP (sorry, don't have a link at the moment). Maxima is general purpose, while PARI-GP is mostly about number theory.

Maxima's history is interesting. It is based on the source code (Lisp!) of the Macsyma system developed at MIT circa 1970-1980. Mathematica is essentially a rewrite of Macsyma with very slightly different syntax. You know what they say about imitation.

I have eaten raw beef before and raw chicken and fish too.

Caution: raw beef and raw fish are probably not that dangerous. Raw chicken stands a nontrivial chance of killing you stone dead. I knew someone who's dead because he cut his hand while preparing chicken to eat.