A corporate firewall where employees can control which sites they want to stay away from. I don't know if this exists. But some companies don't ban some sites

A corporate firewall where employees can control which sites they want to stay away from. I don't know if this exists. But some companies don't ban some sites because they don't want to appear to be too controlling. I personally do this by changing my own /etc/hosts file, but it is too easy to override. A firewall solution my be better for technical and not technical employees to help them to control their own browsing addictions.