Debian is an OS that uses the Linux kernel. Even though it is usually set up on desktop machines, it's being used on a growing number of web servers as well. The reason is that it's very stable, so a server running it won't have to be restarted for months. Debian is also considered to be one of the most protected Operating Systems you can get, because security patches are released within days after an issue is discovered. This is possible because thousands of experienced developers are part of 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 mailing lists and reply within twenty minutes to any kind of question. Thus, 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 several Linux distributions with the highest number of packages - more than 30,000. As the Operating System is completely free to use, you're able to modify both the core and all of the packages in the way you see fit. Also, you will not be required to pay any kind of license fees.