Debian is an Operating System which uses the Linux kernel. Even though it is usually set up on desktops, it's being used on a growing number of web servers too. The reason is that it is very stable, so a server running it won't need to be restarted for months. Debian is also considered to be among the most safe Operating Systems you can get, because security patches are released within days after an issue is discovered. This is possible because thousands of well-trained developers are part of the Debian project on a voluntary basis and not only do they work on the OS itself, they also provide 24/7 support via special mailing lists and respond in twenty minutes to any 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 the Linux distributions with the highest number of packages - more than 30,000. As the Operating System is absolutely free to use, you will be able to modify both the core and all of the packages in the way you see fit. Also, you will not have to pay any kind of license fees.