Debian is a Linux distribution, that is preffered for desktop machines, yet it has been gaining popularity as a server Operating System over the last couple of years too. It's really stable and protected, as fixes are released in just a few days after a problem is discovered. Debian has a large support community, so when you have any kind of questions or troubles with the OS or with any of the 30,000+ packages it comes with, you're able to contact the developers right away through email using special mailing lists and receive a response in just 15-20 min. The Debian community supplies the top level of support possible, because your questions will be handled by the same people that made Debian in the first place, so they have a detailed knowledge of how their own system operates. Since the Operating System is free to use and distribute, no license costs will be included with your hosting fees and you will be able to change the program code files and any other software that you install without any restrictions, to optimize the software environment for your web sites. What's more, Debian performs very well on any kind of hardware, because it is light and effective and does not need a lot of memory.