Debian is an Operating System that uses the Linux kernel. Although it is usually installed on desktop machines, it's being used on more and more web servers too. The reason is that it's very stable, so a server running it won't need to be restarted for months. Debian is also regarded as being one of the most secure Operating Systems nowadays, due to the fact that security patches are released within days after an issue is found. This is possible because thousands of skilled developers work for the Debian project on a voluntary basis and not only do they work on the OS itself, in addition, they provide 24/7 support via special e-mail lists and respond within twenty minutes to any question. In this light, you'll receive 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 several Linux distributions with the highest number of packages - over 30,000. As the Operating System costs nothing to use, you'll be able to modify both the core and all the packages in any way you see fit. Also, you won't have to pay any kind of license fees.