Pivot, a lightweight php-based GPL’d weblogging tool, looks promising. It doesn’t rely on a database backend, which is nice for some of those $4.95/mo hosts that don’t have MySQL in the plan. The Pivot weblog also contains an RSS feed, which is a very good sign.
The setup process appears simple, but I had a few problems with it. I was unable to end up with a working installation, but I only tried it on a testbed and not a server configured for production. I’m impressed with how clean the interface is.