well, I was writing a blog post about it, but it seems Greatpixels couldn't resist not posting
Yes, we rewrote all the codes, and started from zero. you will not see anymore joomlaboard/simpleboard traces there, while keeping the same features (and some more).
The main focus was to have a high speed and low demanding board, the way that when you click on Fireboard you wouldn't see any loading time. As you see, with around 35k members and 50k posts it takes like 0.04 sec to load (on local machine, server is faster). number of queries are dramatically reduced, e.g. the main page take 4 queries, when logged in, and 3 queries for guests. You do the math
Regarding the suppost for content management systems, I should correct that it is not a REAL native joomla 1.5 code, but will support Joomla 1.5 in non-legacy mode, meanwhile supporting Joomla 1.0.x as well (and most probably mambo)
And, forget about the refresh and new! problem. We don't have a primitive method anymore. It is an advanced read/unread control with min. database storage need and MARK read support.
Permissions are group based and as Greatpixels showed, it is pretty flexible.
I will prepare a blog post with more detailed information. keep in touch!
ps. Hey guys, keep here clean from your stuff, would ya?

ps2. Did we mention FireMessage is ready as well?
Cheers