Debian is an OS which uses the Linux kernel. Even though it is usually installed on desktop machines, it is being used on more and more web servers too. The reason is that it's really stable, so a server running it will not have to be restarted for months. Debian is also regarded as being among the most protected Operating Systems out there, because security patches are released within days after a problem is found. 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, in addition, they provide 24/7 support through special mailing lists and reply within twenty minutes to any kind of question. Thus, you'll get an outstanding level of support directly from the developers who know their own platform in depth, and not from a third-party support team. Debian is also among the Linux releases with the highest number of packages - over 30,000. Since the Operating System is completely free to use, you'll be able to modify both the core as well as any of the packages in the way you see fit. Also, you won't have to pay any kind of license fees.