> The thing about Mathematica / the Wolfram language is that it's quite a bit harder to create an open source interpreter than it was for eg R

On the other hand there are lots of Common Lisp systems which are capable of running the venerable Maxima/Macsyma.

> not sure what the status of Octave

I'm glad that Octave and Scilab exist, but I switched to NumPy and never looked back.