Debian is an OS which uses the Linux kernel. Though it is usually installed on desktop computers, it is being used on a growing number of web servers too. The reason is that it's very stable, so a server running it will not need to be restarted for months. Debian is also considered to be one of the most secure Operating Systems you can get, as security patches are released within days after an issue is discovered. 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, they also provide 24/7 support by using special mailing lists and respond in twenty minutes to any question. Thus, you'll obtain top-notch support directly from the developers who know their own platform in depth, and not from a third-party support team. Debian is also one of several Linux releases with the highest number of packages - over 30,000. As the Operating System costs nothing 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 license fees.