Debian is an OS that uses the Linux kernel. Though it is usually set up on desktop computers, it's being used on a growing number of web servers as well. The reason is that it's really stable, so a server running it won't have to be restarted for months. Debian is also considered to be one of the most safe Operating Systems out there, because security patches are released within days after a problem is discovered. This is possible because thousands of experienced developers work 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 mailing lists and respond within 20 minutes to any kind of question. Thus, you'll receive top-notch support directly from the developers who know their own platform in detail, 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. Since the Operating System is completely free to use, you are able to modify both the core and all of the packages in the way you see fit. In addition, you won't be required to pay any kind of license fees.