1. Maple - Version 12. There are some videos (QuickTime format) that give some idea of the product.

   Student version is approximately $100.00 and has most of the functionality of the full release.

2. Mathematica - Version 6. Developed by Stephen Wolfram in 1987. Here is a brief history of the company.
3. Macsyma - Version 2.4 Developed by Symbolics Inc in the late 1960's, and originally written in Lisp.
4. Mu-Pad Pro - Version 4. Originally developed by the University of Paderborn, Germany, it is now bundled with Scientific Notebook and Scientific Workplace, where it replaced Maple as the CAS. However, a free 30 day trial version is available.
5. Live Math and MathEQ.

1. Maxima - Version 5.15.0. Available through sourceforge, under the GPL (GNU Public License)
2. Octave - Version 3.0.1 Available from the GNU organization, it is based on Matlab.
3. SciLab - Version 4.1.2 has freely available binary and source versions available.
4. Gnu Plot - Version 4.2 Interactive graphics software, which supports many operating systems.
5. Reduce General algebraic manipulations.
6. SymbMath (aka Visual Math) is a Java Applet that has symbolic and numerical capability. This link contains documentation and examples.

1. Mu-Pad Lite was offered freely, until 2005.
2. Derive - Version 6.1 Developed by Soft Warehouse, as a successor to muMATH. Bought by Texas Instruments. Discontinued on June 29, 2007 in favor of TI-Nspire.
3. MathCad - Version 14.0 This package originally used Derive (bought by Texas Instruments, and no longer marketed) but now uses Mu-Pad.

Here is an Article entitled A Critique of the Mathematical Abilities of CA Systems, by Michael Wester.