Debian is an Operating System which uses the Linux kernel. Though it is usually set up on desktop computers, it's being used on a growing number of web servers as well. 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 safe Operating Systems you can get, as security patches are released within days after a problem is discovered. This is possible because thousands of skilled 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 by using special e-mail lists and respond within 20 min to any question. In this light, 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 distributions with the highest number of packages - over 30,000. As the Operating System is free to use, you will be able to modify both the core and all the packages in any way you see fit. Furthermore, you won't need to pay any kind of license fees.