Here's a little script that has been created initially to keep track of software bugs. However, it can easily be modified for other types of usage: task assignment, tracking projects, sales quoting system and probably other things as well.
Not many themes around and development it's slow, but I personally love it. When you install it, there's a choice to run it based on MySQL or MySQLi.
Fast, and simple, it runs on my Intranet like a charm - to track sales quotes, taking advantage of the built in notification system.
Download located at FlySpray.org