Debian is an Operating System which uses the Linux kernel. Even though it is usually installed on personal computers, it is being used on an increasing number of web servers as well. The reason is that it is very stable, so a server running it will not have to be restarted for months. Debian is also considered to be one of the most risk-free Operating Systems in existence, because security patches are released within days after an issue is found. This is possible since thousands of skilled developers are working for the Debian project on a voluntary basis and not only do they work on the OS itself, but they also provide 24/7 support via special mailing lists and respond in 20 min to any kind of question. In this light, you will have 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 - over 30,000. As the Operating System is free to use, you are able to modify both the core as well as all the packages in any way you see fit. Also, you won't need to pay any kind of license fees.