Yes, the basic forum is free and there are paid add-ons for extras like private messaging. 

Yes, wpForo is a free WordPress plugin, it doesn't have Pro version and it'll always be free.

We also develop paid addons (separate plugins) for wpForo, they add some extra functions and features to your forum.

Posted by: bulldg

Is this really a free plugin?

It seems so detailed and well formed. Is it really free?

I know, right? wpForo is pretty awesome even without the paid addons. But the paid addons are definitely worth the small fee they charge for them.

Posted by: bulldg

Is this really a free plugin?

It seems so detailed and well formed. Is it really free?

Free as in speech 🙂 You'll not find a better offer anywhere else ! You should encourage the devs though by purchasing some of their add-ons  🙂