Debian is an OS which uses the Linux kernel. Though it is usually set up on personal computers, it's being used on more and more web servers too. The reason is that it is very stable, so a server running it will not need to be restarted for months. Debian is also considered to be among the most risk-free Operating Systems nowadays, because security patches are released within days after a problem is discovered. This is possible because thousands of qualified 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 kind of question. Thus, you'll have top-notch 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 distributions with the highest number of packages - over 30,000. As the Operating System is absolutely free to use, you'll be able to modify both the core and any of the packages in the way you see fit. Furthermore, you won't need to pay any kind of license fees.