I'm sorry if there is another recent conversation, I only found this one.
The forum landscape seems to changed quite a bit in the last couple years with some of the fallout of vB. I wanted to see what people thought about the current options out there from a pure SEO perspective. I agree the best SEO practice is to run a great forum with great content, but once you have that question is how much does your software make a difference? I would think it does make a difference and it's astonishing how many don't follow google's own SEO guidelines.
In my mind these are the leading players at this moment.