All of them! * C, because it is so easy to implement anything you can imagine, there are libraries for everything, and the resulting code runs very fast (altho

All of them! * C, because it is so easy to implement anything you can imagine, there are libraries for everything, and the resulting code runs very fast (although I deliberately limit myself to safe constructs only). * C++, because many things are so much easier (and often safer) to do in C++ than in C, and again you have libraries for everything, and the code runs fast. Modern C++ is quite nice. And you don't have to know all of C++ to write reasonably efficient code. * Python, because there is nothing faster when you need to prepare a prototype, and sometimes the prototype is good enough, especially in io-bound code. * PHP, because you can quickly code practically any web solution extremely quickly (and integrate with any JS framework you like), and the deployment is a breeze. Again, modern PHP has very little in common with the old language you may remember from 2000. * Bash and traditional Unix tools as they allow me to do my job in no time. I took time to learn what each one is for and it just saves time. Yes, I could use Python to grab the first fields from a CSV file but normally I'll do it faster with AWK etc. That said, I love experimenting with new languages like Nim, they are a breath of fresh air and quite fun to tinker with. Nevertheless, in my day to day work, I find myself using proven tools most often.