An open-source kernel, referred as GNU/Linux. Criticised by Windows/Mac users because of it's moderate difficulty of use. Let's hope it's community will continue to be populated by people who have some brain.
Windows fan: Look at my laptop, it's so cool!
Mac fan: Ha! look at mine! (fiddles with GUI)
Windows fan: Yours is shit asdasdasdasdsadasd fuk off
Linux fan: (compiz cube)
Mac fan: HOLY
Windows fan: SHIT