This is an interesting question. I was thinking about something very similar. I was wondering if it would be possible for someone (much smarter than I) to write a more simple version of a message forum that would appear as a blog tab. Users logged in to b2evo would be able to go to and participate in the forums just as they would any other blog.

The blog format is great, but for some purposes a simple forum would work better. I was thinking about submitting this as a suggestion for a plug-in, but since Monarch posed the question here...

phpBB 3.0, which when I last checked is still in beta, will include an option to authenticate users from an outside data source (such as the b2evo users table). You could then just modify your skin files to add a static link to your phpBB installation.

There are ways of hacking phpBB 2.x to authenticate to an outside database, but as someone who's done so a couple of times I assure you that they don't make it easy, and the solutions that I've come up with leave plenty of room for unsynchronized user accounts and/or automatic login problems.

Also, if you look at the roadmap for b2evolution (somewhere in the Docs section) you will see plans for possibly extending b2evo to operate in a forum-like manner.

iirc there is a LDAP module for both bits of software. Worth a look?