Debian is an OS which uses the Linux kernel. Though it is usually set up on desktop computers, it is being used on more and more web servers too. The reason is that it is very stable, so a server running it will not have to be restarted for months. Debian is also considered to be one of the most protected Operating Systems you can get, since security patches are released within days after a problem is found. This is possible since thousands of well-trained developers are part of the Debian project on a voluntary basis and not only do they work on the OS itself, but they also provide 24/7 support through special e-mail lists and reply within 20 min to any question. Thus, you will enjoy an outstanding level of support directly from the developers who know their own platform in detail, and not from a third-party support team. Debian is also among the Linux distributions 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 the packages in the way you see fit. Also, you won't need to pay any kind of license fees.