Debian is an Operating System which uses the Linux kernel. Even though it is usually set up on desktop machines, it is being used on more and more web servers as well. The reason is that it is very stable, so a server running it will not need to be restarted for months. Debian is also regarded as being one of the most risk-free Operating Systems available, as security patches are released within days after an issue is discovered. This is possible because thousands of well-experienced developers work for the Debian project on a voluntary basis and not only do they work on the OS itself, they also provide 24/7 support via special e-mail lists and reply in 20 min to any kind of question. Thus, you'll obtain top-notch 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 - over 30,000. As the Operating System is free to use, you can modify both the core as well as all the packages in any way you see fit. In addition, you will not need to pay any kind of license fees.