GNU/Linux, Virtualization, Cloud ...

You can view the full GNU/Linux family tree on Wikipedia. Choose what suits your needs or whims. Or try everything in virtual computers without even installing if you have a lot of RAM (4GB+) in your computing device as most of the GNU/Linux distributions are 'Live' these days i.e. you can boot up from an ISO image in a virtual computer or boot up your computer from a CD/DVD that is made from the ISO image, using the boot menu that comes up at 'power on' and run the OS.

If you are not ready for any of this, you could at least try GNU and X Windows on a machine with Microsoft Windows by installing CygWin. This may be a good option if you are on a NetBook or on an old PC that needs to stay as is with its original MS Windows installation for family use or some other reason (i.e. not interested in taking risk with network access or other peripherals and their drivers). You will have access to C/C++/PERL/Python compilers/interpreters in a BASH shell environment and run any X Windows GUI programs installed as a part of the CygWin installation (text, vector graphics editors etc.) after starting the X server (shortcut installed in programs menu). You can even do professional typesetting using TeX and its variants. You can build software downloaded from most of the open source projects in this (CygWin) environment.