vBulletin is commercial, as is Invision Community, its primary competitor. phpBB is pretty badly dated. It still works but it's clunky and development has been

vBulletin is commercial, as is Invision Community, its primary competitor. phpBB is pretty badly dated. It still works but it's clunky and development has been very slow. (The last major release was four years ago; everything since then has been minor maintenance.)