Recognized as the first true alt-coin based on a fork of the Bitcoin source code, Namecoin is an alt-coin that implements extensions in its blockchain to allow the recording of public name information for various applications. The first of these applications was a substitute for the Internet's domain name system (DNS).
The DNS is similar to a large phone book. When you type google.com into your Web browser, a request is made to the DNS servers asking to resolve the name to an IP address. The IP addresses are used to route information between two computers on the Internet, similar to the way the telephone system connects two phone numbers together.
With the original DNS system, the centralized authorities had established issue names, such as google.com or wikipedia.org, to organizations. Once purchased, the organization could modify the list of servers that their domain names resolved to.
There are some controversial issues with relying on central authorities...