Debian is an OS which uses the Linux kernel. Though it is usually set up on desktop computers, it is being used on more and more 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 regarded as being among the most protected Operating Systems you can get, as security patches are released within days after an issue is found. This is possible since thousands of qualified developers are employed by 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 reply in 20 min to any question. Thus, you'll enjoy 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 among the Linux releases with the highest number of packages - more than 30,000. Since the Operating System is completely free to use, you'll be able to modify both the core as well as all the packages in any way you see fit. Also, you won't be required to pay any license fees.