Debian is a Linux release, that is widely used for desktop computers, but it's been gaining popularity as a server Operating System during the last couple of years too. It's really stable and secure, as fixes are released in a few days after a problem 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 comes with, you're able to contact the developers immediately via electronic mail using special mailing lists and receive a response in just 15-20 min. The Debian community gives you the best level of support possible, since all your questions will be handled by exactly the same people who built Debian in the first place, so they have an exhaustive knowledge of how their own system operates. As the Operating System is free to use and distribute, no license charges will be added to your hosting fees and you'll be able to change the program code files and any other software which you install with no restrictions, so as to optimize the software environment for your web sites. Furthermore, Debian performs really well on any kind of hardware, because it's light and efficient and does not need a lot of memory.