Debian is a Linux distribution, that is preffered for desktop machines, however it's been becoming more popular as a server OS during the last couple of years as well. It is very dependable and secure, as fixes are released within a couple of days after an issue is discovered. Debian has a huge support community, so when you have any questions or issues with the OS or with any of the 30,000+ packages it includes, you are able to contact the developers immediately through e-mail using special mailing lists and receive a reply within 15-20 min. The Debian community gives you the best level of support possible, as your questions will be handled by exactly the same people that made Debian in the first place, so they have an exhaustive knowledge of how their system works. Because the Operating System is 100% free to use and distribute, no license costs will be added to your web hosting fees and you can modify the program code files and any additional software that you install without restrictions, to optimize the software environment for your web sites. What's more, Debian performs very well on any hardware, as it is light and effective and doesn't need much memory.