Debian is an Operating System which uses the Linux kernel. Even though it is usually set up on personal computers, it's being used on a growing number of web servers too. The reason is that it is really stable, so a server running it will not need to be restarted for months. Debian is also regarded as being one of the most safe Operating Systems nowadays, because security patches are released within days after an issue is found. This is possible because thousands of qualified 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 twenty minutes to any kind of question. Thus, you will get top-level 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 - more than 30,000. As the Operating System costs nothing to use, you can modify both the core and any of the packages in the way you see fit. Furthermore, you will not have to pay any kind of license fees.