Okay, I thought I misunderstood the topic, but apparently I didn't.

I administrated a vBulletin forums for roughly 10 years. We started out as a 3.x, but I was foolish and upgraded to 4.0 in the second or 3rd year and screwed a lot of stuff I programmed for it, heh...

But anyways.

vBulletin is built with a lot of "hooks" where you can make a "plugin" to do virtually ANYTHING.

I programmed Triple Triad onto my forum--no bullcrapping here. Except I made it where one certain usergroup could "create" cards, given a PNG with transparent background, and had an interface for them to input numbers, elements, etc.

I programmed a "Mafia" game where you could ONLY see certain threads if the game I auto-programmed into it assigned you a certain "Role" in Mafia.

I programmed so much more for that forum, and I can confidently say, as I was a 1-man-team back then, what the OP is asking for would neither require much time nor much money. In fact, they have several such plugins (with support) at vBulletin.org.

I chose vBulletin in fact BECAUSE it was so customizable, even with third-party stuff, instead of getting something free.

They really COULD do so much more with these forums with not that much effort.

The could program filters in, too.

Or people could just tag threads properly. (I'm guilty.)