WebRTC allows browsers to communicate directly with each other without the data having to be relayed through a server.
It is also encrypted in the browser using DTLS (a derivative of SSL) ensuring you can communicate with anyone in total privacy. What's so exciting about another video chat system (WebRTC) when we already have Skype? you may well ask. After microsoft bought skype from Silver Lake Partners for $8.5 billion in 2011 they ditched the peer to peer system - supposably because of scalability issues but the slightly paranoid believe that this now makes it easier for the NSA to snoop on conversations which previously (in the peer to peer system) was impossible. A good article about this:
A technical explanation of WebRTC can be read here.