Open source web protection/restrictions?

[Fcx35x10]

Hello community

I'm currently assigned a task from a family friend who is opening up a restaurant soon. They want to be able to restrict their employee's internet browsing access from the PoS/PC machines, blocking sites such as facebook, emails, etc. In the past I used K9 Web Protection. It's pretty simple and free to use; however, I was wondering if there's anything better out there that's a little more professional but still free