I am currently working on installing mediawiki and integrating users with phpBB3 and WordPress. I have them somewhat integrated, in that you cannot create a new user under the wiki, just under the forum, but logging in to one does not automatically log you into the other. I had this working years ago, but much has changed since then and many of the mods/extensions haven't been updated. There's one more phpBB3/mediawiki SSO extension I need to try. If it works, I'll use it, as it is MUCH better, but if not, I'll use what I have for now. At least it gives me a starting point.
Also, I need to integrate the themes. The phpBB3 theme integrates fairly well, but I still need to tweak it just a little bit. The wiki is close as well, but still needs considerable tweaking to make it fully integrated. I'll work on that once I get the functionality finished.