This is a Chrome Extension aimed to improve productivity.

Usability of sites is reduced so that users will spend less time on distracting sites. Currently, the extension only blocks Facebook, Twitter, and Tumblr. Future releases plan to have user-defined sites to block.

The extension is free to download here: https://chrome.google.com/webstore/detail/dogestracted/cpognobmhggliigkkcfdoabecbngajjl?hl=en-US