Debian is a Linux distribution, which is widespread for desktop computers, however it's been gaining popularity as a server Operating System over the last couple of years as well. It's very stable and secure, since fixes are released in just a few days after an issue is discovered. Debian has a vast support community, so if you have any kind of questions or problems with the OS or with some of the 30,000+ packages it is equipped with, you can easily contact the developers directly through e-mail using special e-mail lists and receive a reply within 15-20 minutes. The Debian community offers the best level of support possible, because your questions will be handled by the very same people who made Debian in the first place, so they have a thorough 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 can modify the code files and any other software that you install with no restrictions, so as to optimize the software environment for your sites. Furthermore, Debian performs really well on any hardware, as it's light and efficient and does not require much memory.