Debian is a Linux release, which is widely used for desktop computers, but it has been gaining in popularity as a server Operating System over the last few years too. It's really stable and secure, because fixes are released within a couple of days after a problem is discovered. Debian has a vast support community, so if you have any questions or troubles with the OS or with any of the 30,000+ packages it is equipped with, you can easily contact the developers right away via e-mail using special mailing lists and receive a response within 15-20 minutes. The Debian community gives you the best level of support possible, since all of your questions will be handled by the very same people that made Debian in the first place, so they have a detailed knowledge of how their own system works. As the Operating System is 100% free to use and distribute, no license charges will be included with your web hosting fees and you'll be able to customize the program code files and any other software that you install without restrictions, in order to optimize the software environment for your web sites. Furthermore, Debian performs very well on any kind of hardware, as it's light and fast and does not need a lot of memory.