BitDNS

In September 2010, a proposal was made on the BitcoinTalk forums about a DNS protocol that would rely on Bitcoin. A quick description of this project is provided here from the bitcoin.it wiki:
Bitdns was a project with the goal to extend Bitcoin's technology to a domain name service, expanding the software to support transactions for registering, updating, and transferring domains. The project eventually became an altchain with its own altcoin, known as Namecoin.