Debian is an OS that uses the Linux kernel. Though it is usually set up on desktop computers, it is being used on an increasing number of web servers too. The reason is that it's very stable, so a server running it won't have to be restarted for months. Debian is also regarded as being among the most protected Operating Systems available, since security patches are released within days after a problem is found. This is possible because thousands of skilled 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 e-mail lists and respond within 20 min to any kind of question. Thus, you will have top-notch 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 - more than 30,000. As the Operating System is absolutely free to use, you are able to modify both the core as well as all of the packages in the way you see fit. Also, you won't need to pay any license fees.