I have been a huge fan of SMF (Simple Machines Forums).
There was a time when SMF played nice with all other popular CMS'.
Today, it is no longer this way. Actually, it's been a few years now. I have come to terms with it. I have tried using other CMS' in conjunction with SMF and at the end of the day, why have two separate databases? So, I opted to go with SMF/Portal and use this as a make-shift CMS/Forum. I know that it's not as stylish as a WP theme or Joomla theme, but Joomla is a bit of a script-kiddies play ground known for it's vulnerabilities and WP is not even really a CMS but can be used as one (this is an argument that is left open to debate) To me WP is more than a blog, if you know what you are doing and can find a good theme to work with and thus can be considered a CMS.
I have tried other Forums and just was not happy with the results.
And so, I stay with SMF and portal up.
In closing, SMF+Portal reminds me of the old school PHP-NUKE
I know, right? It was always fun back then and I guess this is why I enjoy SMF+Portal system.
Just me and some random thoughts.