Debian is an OS which uses the Linux kernel. Even though it is usually installed on personal computers, it is being used on a growing number of web servers as well. The reason is that it is really stable, so a server running it won't have to be restarted for months. Debian is also considered to be among the most risk-free Operating Systems out there, due to the fact that security patches are released within days after an issue is found. 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, but they also provide 24/7 support through special e-mail lists and respond in 20 min to any kind of question. Thus, you'll receive top-notch 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 the Linux releases with the highest number of packages - more than 30,000. Since the Operating System is free to use, you can modify both the core as well as any of the packages in any way you see fit. Furthermore, you won't be required to pay any kind of license fees.