StayFocusd – A free Google Chrome plugin that helps you limit your time online by letting you block certain websites, subdomains, specific paths, specific pages, and even specific in-page content such as videos, games, etc.
LeechBlock – A plugin that can help increase your productivity by creating set of blocking rules for different situations. These sets can block fixed time periods, after a time limit is done, or a combination of the two. You can also set a password to help you block the internet in important times. Available on Google Chrome and Mozilla Firefox.
Cold Turkey – A highly customization Windows application that can help increase productivity for everyone. It includes the ability to block specific pages, block the entire internet, set a timer, give you statistics on your productivity, schedule no-internet times, block applications, and lock the computer to get you to take a break from work.
Freedom – A productivity app that works with multiple devices by blocking apps and websites on them according to the specified blocking terms you have given. That way you cannot circumvent your measures in getting focused by switching to another device. It is available on Mac, Windows, iOS, Google Chrome, Mozilla Firefox, and Opera.
SelfControl – An free open source application for Mac that blocks your access to distracting internet programs and websites. You can set a time period to block and add specific sites to blacklist. This app continues to block internet access at the scheduled time block even if you decide to restart or delete the application.