The turning point in Unix's history came when it was reimplemented almost entirely in C during 1972 - 1974, making it the first source-portable OS. Unix subsequently underwent mutations and expansions at the hands of many different people, resulting in a uniquely flexible and developer-friendly environment.
By 1991, Unix had become the most widely used multi-user general-purpose operating system in the world. Many people consider this the most important victory yet of hackerdom over industry opposition (but see Unix weenie and Unix conspiracy for an opposing point of view). Unix is now offered by many manufacturers and is the subject of an international standardisation effort with the Unix trademark being owned by X/Open. Unix or Unix-like operating systems include OSF, Version 7, BSD, USG Unix, Xenix, Ultrix, Linux, and GNU.