The forums that Josh offers with his hosting packages are free I believe. Those are invision board and phpbb. Both of these are forum software packages.

Josh’s hosting solutions are not free how ever. If your running your site on a free host you may or may not be able to run your own message board. (most likely not)

You’ll need a host that supports php and mysql databases. (well there are other solutions that can do without php and mysql but I can’t think of any off the top of my head)

Hope that helps some.