Look no further, this is THE WordPress forum software.

Thought I’d found the ideal plug-in with another-author until a very nice man said I needed to pay 99 of his American dollars before I could add a subscription check box or an upload image/file button.
I then tried the “too good to be true” bbPress and haven’t looked back.
I’ve had to look sideways a couple of times due to minor issues but these where resolved quickly thanks to the excellent after-download support.
Thanks to all involved with this products development.