Namecoin was the first fork of the Bitcoin, making it the very first "altcoin". In the same way that the Bitcoin experiment freed money, the goal of the Namecoin project was to free Domain Name Service (DNS). For example, instead of buying a domain like, "mysite.com", you could buy a domain like "mysite.bit". It may seem like there is not much difference between the two of them, when in fact, there are worlds apart.
When you buy "mysite.com", you really only buy the right to use the domain name for as long as you continue paying for it. Several international, non-governmental bodies have to power to take your "mysite.com" domain from you for what ever reason they want to.
When you buy "mysite.bit", you pay about 1/100 of the price of "mysite.com" and you pay it only one time and the domain is yours for life. All domain name information, including domain ownership, and personal identification, are stored in the Namecoin blockchain and can never be changed, unless the owner himself decides to change it. In addition to this, because the ownership is if controlled by the blockchain, no one can ever take the domain away from the owner.