MyBB Community Forums

Are there any public ones for free? Or are they all custom scripts?

For what?

If you mean MyBB Auto-installlers, BMR777 has a script.

http://rusnakweb.com/mybbmultiforums.php

You can check out Softaculous. I used them for a while until I found some serious bugs (which they apparently fixed) and bought a few Installatron licenses.

I think he means MyBB auto installers.