Debian is a well-known Linux distribution, that is used mainly on PC's, but lots of people have started using it lately as a web server OS as well, due to the stability and protection it offers. The latter is a direct result the fact that Debian is developed and supported by countless qualified volunteers all around the world, which means that any patch that's needed to fix a particular issue is released in a couple of days. The very same community will also help you with any question or problem that a user may ever encounter, since they can be contacted through electronic mail using mailing lists and a qualified response will be sent in no more than 15-20 minutes. The advantage here is that all your queries will be responded to by the same people who have developed the Operating System itself and they have a detailed knowledge of how it works. As Debian is provided for free, you won't have 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 which are available for it.