That's easy, every time I did something new I learned a lot. First time + Linux. + Shell scripting. + Grep, regex + Embedded development, configuring ADC h

That's easy, every time I did something new I learned a lot. First time + Linux. + Shell scripting. + Grep, regex + Embedded development, configuring ADC hardware, e.g. + FPGA, designing FSMs, adders, etc. + Reverse engineering anything. Use a logic analyser. I just learned the details on HDMI a week ago, for example. + Vim, and sticking to it in the beginning. :-) + Basic sysop stuff, ssh, rsync, dig, etc. + Cuda. + Tensorflow. + Javascript. Definitely if you come from a C angle. Playing with modern frameworks doesn't hurt! Of course those are not just tools, but they all help understanding what's the best tool for the job. :-)