We are looking at the possibility of moving the official forums to the server and using more versatile forum software. Migration of the current forum software is essential, as is keeping a threaded forum. In the meantime, you may note some changes on these forums as we consider different strategies.

The Ask an Immortal forums may not remain separate forums on the new site. I would be interested in hearing player feedback regarding consolidation of those forums into a single Ask an Immortal forum.

http://en.wikipedia.org/wiki/Comparison_of_Internet_forum_software

If you're aiming for threaded forum software, your best bet is probably vBulletin (most prominent one used with threads) although I've heard decent things about Invision Power Board.