Debian is an Operating System that uses the Linux kernel. 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's very 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, due to the fact that security patches are released within days after an issue is discovered. This is possible since thousands of well-experienced 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 respond in 20 min to any kind of question. Thus, you'll receive 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 costs nothing to use, you are able to modify both the core and all of the packages in the way you see fit. Furthermore, you won't have to pay any kind of license fees.