Debian is an Operating System that uses the Linux kernel. Even though it is usually installed on desktop machines, it is being used on more and more web servers too. The reason is that it's really stable, so a server running it will not need to be restarted for months. Debian is also considered to be one of the most secure Operating Systems you can get, as security patches are released within days after a problem is discovered. This is possible since 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 by using special mailing lists and respond in 20 min to any question. Thus, you'll obtain 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 releases with the highest number of packages - over 30,000. As the Operating System is completely free to use, you will be able to modify both the core and any of the packages in the way you see fit. In addition, you will not need to pay any license fees.