At the systems level, C compiler and POSIX API are pretty much a given. Once you venture beyond that the platforms start becoming very different. But you coul

At the systems level, C compiler and POSIX API are pretty much a given. Once you venture beyond that the platforms start becoming very different. But you could note that except for Microsoft Windows, all the other environments you mention are basically variants of Unix. So you will find pretty much the same facilities if you stay close to the hardware level - which in my lexicon is what systems level is all about. If you need a GUI, you could consider that HTML5 compliant browsers are everywhere. You would only need to write a minimalist web server (there are hundreds of examples around) to interface your systems level stuff to a user interface. Perhaps if you gave some more information you'd get more pertinent suggestions. Why neglect the literature? How can you expect to write systems level stuff without a solid foundation of knowledge????