My question is concerned with the idea of putting on your resume that you know a official language but have mostly experimented with its open-source counterpart (Example: putting down you know MATLAB but you know Octave which is almost similar to MATLAB). Also I plan to learn other languages like Mathematica and IDL and SPSS but I have found their open source free counterparts and I have been wondering if I can practice with the open-source software and then put down on my resume that I know the "offical" programming language.
Any feedback would be much appreciated.
Just be honest about the software you're skilled with, and let the potential employer decide if you fit the position.
Nothing is preventing you from applying to a visual studio .net developer position even though you're a mono power-user ; but don't lie about being already trained at using VS if you aren't, it's a sure of way of not getting hired IMO