Liberty Arrow by Gary Hilares

Liberty Arrow is a simple and elegant way to block distracting websites. Apart from the features which most page blockers have, Liberty Arrow also has: Unlimited sites, a substring blocking system and password protection.

Detailed feature description:

• Unlimited sites: You can have as many blocked pages as you want. The only restriction is the storage space itself.
• Substring blocking system: You not only can block sites by adding the domain name, but also by adding any url's substring. For instance, you can add a Youtube playlist's id to your blocked pages and that playlist will be blocked. You can also add the domain and, because of this feature, all subdomains will be blocked as well.