there are plenty but as i asked earlier what languages/database will you be using? if it is a free host i doubt you will have mySQl etc so having a remotly hosted one is prolly your only option - on paid sites you may have the requirments to host your own and many also provide pre-built scripts
if you are looking for one of your own however you could try ::
hotscripts.com

or if you want to build an actual forum there is loads of ones out there
phpBB
yaBB
phpNuke
Invision
exoops

etc etc

without knowing your exact requirments is hard to give an exact answer

v_Ln