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One of the great things about Linux, when compared with proprietary operating systems such as OS X and Windows, is that the licenses under which it is released allow developers to modify it and create new versions suited to their particular needs. Because of this, there are hundreds of varieties of Linux available, most of them tuned to very specific and niche requirements, while a small subset of distributions (or distros) have become very popular.
Of course, the most successful of these is Ubuntu, which itself is based upon another well-liked distro called Debian. But some developers have now taken Ubuntu and created derivatives of it for their own needs. For example, there’s Ubuntu Studio for creating media, Edubuntu for use in education, Mythbuntu for using as a personal video recorder, and so on.