Debian is an Operating System which uses the Linux kernel. Although it is usually set up on desktop machines, it's 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 regarded as being one of the most secure Operating Systems to choose from, since security patches are released within days after an issue is discovered. 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, they also provide 24/7 support by using special e-mail lists and respond within twenty minutes to any question. Thus, you'll receive 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 one of the Linux distributions with the highest number of packages - over 30,000. As the Operating System costs nothing to use, you can modify both the core as well as all the packages in any way you see fit. Also, you won't have to pay any kind of license fees.