Debian is an Operating System that uses the Linux kernel. Although it is usually installed on personal computers, it's being used on an increasing 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 safe Operating Systems nowadays, as security patches are released within days after an issue 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, they also provide 24/7 support through special mailing lists and respond within 20 min to any question. Thus, you'll obtain an outstanding level of 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 several Linux distributions with the highest number of packages - over 30,000. As the Operating System is free to use, you are able to modify both the core as well as any of the packages in any way you see fit. Furthermore, you will not need to pay any license fees.