There are a lot of parental controls available on the market with different functionality built-in. Common use cases of such software include parents who wish to limit what sites their children may view from home computers, and employers restricting what content may be viewed by employees while on the job. The most famous are Net Nanny, Ez Parental Control and Sentry Parental Controls.
Some parental control software such as Ez Internet Timer includes time control functions that empowers parents to set the amount of time that child may spend accessing the Internet or playing games or other computer activities
Other parental control software such as 8snaps.com work on gaining visibility and feedback into childrens online activities as opposed to implementing blocks or filters.