Debian is a Linux distribution, which is widespread for desktop machines, yet it's been gaining in popularity as a server Operating System over the last couple of years as well. It is very dependable and protected, as fixes are released in just a few days after an issue is discovered. Debian has a vast support community, so when you have any questions or troubles with the OS or with some of the 30,000+ packages it includes, you can easily contact the developers straight away through electronic mail using special mailing lists and receive a response in just 15-20 minutes. The Debian community gives you the top level of support possible, as your questions will be handled by the same people that built Debian in the first place, so they have an in-depth knowledge of how their own system functions. Since the Operating System is 100% free to use and distribute, no license costs will be included with your hosting fees and you'll be able to change the code files and any other software that you install with no restrictions, to optimize the software environment for your sites. Furthermore, Debian performs very well on any hardware, as it's light and efficient and doesn't require much memory.