Debian is an OS which uses the Linux kernel. Even though it is usually installed on desktop machines, it is being used on an increasing number of web servers too. The reason is that it is really stable, so a server running it won't have to be restarted for months. Debian is also regarded as being among the most safe Operating Systems available, since security patches are released within days after an issue is found. 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 in 20 minutes to any kind of question. In this light, 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 among the Linux distributions with the highest number of packages - over 30,000. Since the Operating System costs nothing to use, you are able to modify both the core and any of the packages in any way you see fit. Also, you won't need to pay any license fees.