Wired - Super Kiwi Cloak, a GTD (Getting Things Done) tool that helps you focus by blocking access to certain websites during work hours, yet allows hourly breaks.
[Similar to LeechBlock for Firefox that blocks time-wasting websites]
Helps you focus on GTD by blocking access to all “Included Pages” during work hours. Because a script is so easy to get past, this script also allows you to browse freely during a defined period each hour. The goal is to stay on task, by giving you less incentive to break your rules.
By default, the script is set to block access from 9am to 5pm, to allow you to access sites during a ten-minute window at the top of each hour (from 5-till to 5-after), and to only run on weekdays. These settings can all be changed within the script.
You can block a page by adding it to “Included Pages” or whitelist it by adding it to “Excluded Pages” through the “Manage User Scripts” menu. You can also block all pages (except whitelisted ones) by adding * to the “Included Pages”. Link.