What is the best computer algebra system
 

Hello, I'm going to study physics and therefore need a computer algebra system. I wanted to ask you what is the best freely available cas for linux.

I got a whole bunch of results just by googling "linux computer algebra system". The most widely used ones are paid subscriptions (Matlab & Mathematica). Here's the top few hits:

http://maxima.sourceforge.net/
http://www.bway.net/~lewis/
http://www.sai.msu.su/sal/A/1/index.shtml

If your university has a subscription to Matlab or Mathematica, you can probably just ssh into a machine and use the programs...