Doman Name System (DNS) is a technology that translates URL names into IP addresses, without DNS it would be impossible to type an easy to remember name in our browser toolbar we would be forced to remember computer IPs instead. DNS censorship is one of the most used systems to block websites, since all domains have to resolve in a nameserver it is possible to impede all request for a certain website on the central server, some ISPs in Europe already use this system to block websites serving what they consider to be child pornography and ISPs in China or Iran also use DNS blocking as part of their Internet filtering efforts. One way around is changing the default ISP DNS servers by unfiltered ones, if you would like to use a VPN in China, you should use something like Comodo DNS or it possibly won’t work.
Big multinationals running their own DNS servers block access through their network to websites that breach the company IT policy. It is possible for an IT department or ISP to serve a page not found or time out message when you attempt to visit a specific URL, they might or might not inform you that the page is blocked, it is up to them, they can even show you a fake page.
ODDNS (Open and Decentralized DNS) is an open source (GPL3) Peer-to-Peer DNS system that can act as an alternative or complement the conventional DNS system, webmasters can install it at home in their own computer, ideally a dedicated one, depending on load. ODDNS enables communication with other DNS servers working as a P2P client and server at the same time, there is no root server or domain registration authority (ICANN) involved in the running of the nameservers, only users.
The idea of using a decentralized DNS system is to stop censorship from any Government in the world and eliminate domain registrars, this makes domain seizure and blocking of websites impossible. Anyone running ODDNS can create and maintain his own domain name for free, the project success relies on the number of people running ODDNS in their computers.
Visit ODDNS homepage
UPDATE 2013: Website not loading for months, it seems the project died, link erased.