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 really stable, so a server running it won't 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 an issue is discovered. This is possible because thousands of qualified developers are working for the Debian project on a voluntary basis and not only do they work on the OS itself, but they also provide 24/7 support by using special e-mail lists and reply within 20 minutes to any question. Thus, you'll 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 - over 30,000. As the Operating System is absolutely free to use, you're able to modify both the core as well as any of the packages in any way you see fit. In addition, you will not have to pay any license fees.