Habari is an open source blogging platform that runs on top of PHP. I thought I would give it a go for a few side projects since WordPress and WordPress mu (soon to merge) was getting overly kludgy. Harabi states on their website that their stable build isn’t really all that stable 
. It’s more of a Beta than a release, so I wouldn’t run anything production on it.
To me, Habari looks like what the WordPress would have created if they could go forward into time to look at the beast they have created. The best part of Habari is how lite it is, and how well set out everything is. Habari setup is straight forward and can be pointed at several different types of database servers. Less than 5 minutes and I had a blog up and running. Another 2 minutes and I had a second blog running off the same install. With the set out of the system you can make changes that apply to all or just one. It’s very light and simple to use. It appears that the community is making tones of great themes and plugins and I find that Habari will grow to point it takes over WordPress. As long as it doesn’t become kludgy like WordPress, I think it’s a great competitor.