Debian is a popular Linux distribution, that is used primarily on desktop computers, still many people have begun using it lately as a web server OS too, due to the stability and protection it offers. The latter is a consequence of the fact that Debian is developed and supported by thousands of qualified volunteers all around the world, so that any patch which is needed to fix a particular issue is released in a couple of days. The same community will also help you with any question or issue that a user may ever experience, because they can be contacted via electronic mail using mailing lists and a competent response will be sent in no more than 15-20 min. The advantage here is that your questions will be answered by the same people who have created the Operating System itself and they have a detailed knowledge of how it functions. As Debian is provided for free, you will not need to pay any kind of license fees to use it and you will be able to customize it as much as you want or need. This is valid for the Operating System and the 30.000+ software packages that are available for it.