Debian is an Operating System which uses the Linux kernel. Though it is usually installed on desktop machines, it's being used on more and more web servers as well. The reason is that it's really stable, so a server running it will not have to be restarted for months. Debian is also regarded as being among the most protected Operating Systems out there, as security patches are released within days after an issue is discovered. This is possible because thousands of well-trained developers are part of 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 min to any kind of question. Thus, you'll have 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 several Linux releases with the highest number of packages - over 30,000. Since the Operating System is absolutely free to use, you can modify both the core as well as all the packages in any way you see fit. Also, you will not need to pay any kind of license fees.
