Not sure exactly what you are looking for but here are a couple suggestions. They are not toys and don't hold your hand, but there is a lot of documentation online and in books and youtube videos. Of the three below I like iPython the best. But they are all free. They are all notebook style programs so they can produce very nice documents with graphics and mathematical typesetting through latex.
GNU Octave is something like MatLab.
https://www.gnu.org/software/octave/
iPython can do a lot but requires some knowledge of the Python programming language, but can also be programmed to a less extent in other programming languages. I like the Anaconda version because it is very simple to install and maintain. It can also format mathamatics using latex.
iPython has many specialized libraries. For instance:
R is mainly for statistics (I think).
https://www.r-project.org/
Never really used it but it looks very nice.
If you have a raspberry pi, there is a free version of Mathematica and Wolfram Language.
http://www.wolfram.com/raspberry-pi/
I have used this on an older pi which was a little slow but usable, the newer Raspberry Pi versions should be a lot faster. You can use your regular computer to ssh or vnc into the pi. There are lots of youtube tutorials on how to do this.
I don't know much about SAGE but here is a link.
http://www.sagemath.org/
I think that SAGE is mainly for symbolic math.