Debian is an OS that uses the Linux kernel. Even though it is usually set up on desktop machines, it's being used on a growing number of web servers as well. The reason is that it's very stable, so a server running it will not need to be restarted for months. Debian is also considered to be among the most safe Operating Systems nowadays, since security patches are released within days after a problem is found. This is possible since thousands of qualified developers are employed by 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 reply in 20 minutes to any kind of question. In this light, you will enjoy top-level 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 - more than 30,000. Since the Operating System is absolutely free to use, you'll be able to modify both the core as well as any of the packages in any way you see fit. In addition, you won't need to pay any kind of license fees.