Debian is an Operating System that uses the Linux kernel. Even though it is usually installed on desktops, it is being used on an increasing number of web servers as well. The reason is that it's really stable, so a server running it will not have to be restarted for months. Debian is also considered to be among the most secure Operating Systems nowadays, since security patches are released within days after a problem is discovered. This is possible because thousands of well-trained developers are working 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 through special mailing lists and reply within 20 min to any question. Thus, you'll receive 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 one of the Linux releases with the highest number of packages - over 30,000. Since the Operating System is completely free to use, you will be able to modify both the core and all the packages in any way you see fit. In addition, you won't have to pay any kind of license fees.