Debian is an OS which uses the Linux kernel. Even though it is usually installed on desktop computers, it's being used on an increasing number of web servers as well. 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 among the most secure Operating Systems out there, as security patches are released within days after a problem is discovered. This is possible since 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 via special e-mail lists and respond in 20 min to any question. In this light, 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 one of the Linux releases with the highest number of packages - more than 30,000. As the Operating System is completely free to use, you can modify both the core and all of the packages in the way you see fit. Furthermore, you won't be required to pay any license fees.