If you're going to mention Maxima, you should be aware that an actively developed open-source program collection called Sage (http://www.sagemath.org/) uses Maxima as well as many other open-source packages to create a rich mathematical environment that's becoming increasingly popular.

Sage uses Maxima internally to generate symbolic results, but Sage also has many other integrated math tools, and has a Web 2.0 interface -- a server-enabled front end.

My Sage tutorial: http://arachnoid.com/sage