Debian is an Operating System which uses the Linux kernel. Although it is usually set up on desktops, it is being used on a growing number of web servers too. The reason is that it is 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 protected Operating Systems to be found, since security patches are released within days after an issue is found. This is possible since thousands of well-experienced 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 by using special mailing lists and respond within 20 min to any question. In this light, you will 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 - over 30,000. As the Operating System is completely free to use, you are able to modify both the core and all of the packages in the way you see fit. Also, you won't need to pay any kind of license fees.