MATLAB and Simulink
MATLAB was my first programming language that I've learned and retained. Previously I've used JavaScript and some Labview, but that was in middle school. As I advanced in my college career I had to use MATLAB... But there were no courses to formally teach it. Therefor I went to some additional courses offered by WPI and learned through 'trial by fire'. I often resorted to Mathwork's comprehensive documentation to resolve issues.