Debian is an Operating System that uses the Linux kernel. Though it is usually installed on personal computers, it is being used on more and more web servers too. The reason is that it's really stable, so a server running it will not need to be restarted for months. Debian is also regarded as being one of the most protected Operating Systems out there, as security patches are released within days after an issue is discovered. This is possible since thousands of qualified developers work for the Debian project on a voluntary basis and not only do they work on the OS itself, but they also provide 24/7 support via special e-mail lists and respond in twenty minutes to any kind of question. In this light, you'll get top-level support directly from the developers who know their own platform in detail, and not from a third-party support team. Debian is also one of the Linux releases with the highest number of packages - more than 30,000. As the Operating System costs nothing to use, you'll be able to modify both the core as well as all of the packages in the way you see fit. In addition, you won't have to pay any kind of license fees.