In 1992, linus torvalds decided to make his own operating system based on unix, only he released it for free, allowing others to add onto the code, making it better, under the condition that they must give back to the project. FreeBSD was also a recreation of unix, back in the 80's.
yeup!
most servers on the internet run on Linux, and the link I posted gives you some info about how file permissions work on Unix/Linux operation systems.... gives you all basic info you need to understand WHY a file can be edited by someone or not...