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Forum Moderators: rogerd
The most search-engine friendly forum software that I know of is WebBBS. However, that's about all that can be said about this particular package, since it has not been updated in years.
Because of WebBBS's lack of basic modern facilities, I recently abandoned it in favour of vBulletin. I don't regret the move for a number of reasons, but one thing that has worsened for my forum is search-engine ranking. Posts that were at the top of page one in Google with WebBBS are down the middle of page two with vBulletin.
There are always pros and cons in any choice. But I'm hoping that vBulletin will get its act together someday soon.