If you have a few dollars
MuPAD is extremely well priced compared to Mathematica, Maple and MathLab.
Following are free and open source versions for those of us no longer getting student discounts.
Sage – installs, extends and provides a front end for Maxima ( It’s a great way to get Maxima installed and running easily on your computer, versions for Win/Linux/OSX )
Maxima has native Windows and Linux Code. ( Instructions for getting it up and running on OS X )
SciLab There are downloads for Windows and Linux and a link to an OSX version.
Axiom has Linux and Windows versions and
OS X instructions
Yacas should word on all operating systems.
Octave has OSX, Linux and Windows versions.
Euler has Linux and Windows versions. It should work on OS X as well.
A link list of other open source computer algebra programs including Jasymca so you can derive and integrate on your mobile smart phone.
Because these software packages are open source you should be able to download and compile any of them for your computer if a binary version is not available.
See also on this site:Useful math websites