Parental control filters have a reputation for charging a lot and giving back very little in return. Sometimes, they literally don't give enough back, and have been known to block completely clean sites.
ParentalControl Bar isn't perfect--like its cousins, it blocks some sites that shouldn't be obstructed, and occasionally allows sites that should be blocked. However, the price is right--it costs nothing. Not only does it not extort parents for its services, it allows parents to approve sites both on the fly and via a "Blocked history" list.
The app is small, just over 1MB. The toolbar interface allows parents one-click switching from Parent to Child mode by clicking a button, which changes from red to green. To switch back--or to use any of its nonblocking functions or view a blocked site--a password is required.
Despite claims to the contrary, the program doesn't support Firefox 2, although it does work fine on Internet Explorer 7. For parents looking for a cost-effective tool to help give their children a bit of controlled freedom on the Internet, ParentalControl Bar is a safe way to go.