Open source maths packages
It's been a long time since I was actively researching maths, but even then there was (and still is) a fantastically fast number-theory based CLI environment called PARI/GP (sudo apt-get install pari-gp) http://pari.math.u-bordeaux.fr/ and a massively comprehensive algebra package called GAP [Groups Algorithms and Programming] (sudo apt-get install gap) http://www.gap-system.org/ . Both still being actively developed.
They didn't have the GUI or comprehensive coverage that Mathematica or Maple had then but they covered their own fields pretty damn well. I daresay there are other packages for other areas of maths.
Having said that, not really very school-pupil friendly unless you're already a programmer.
I guess the problem, in the field of pure maths at least, is that once it is known a solution exists the researcher loses interest in actually finding it, so once there's a CLI, they lose interest in actually building a GUI on top (that's just /bookwork/)! ;)