I was wondering if anyone could offer some recommendations on billing / time tracking software? I'm looking for something simple to keep track of hours spent on projects for me and 3 other employees. I'd really like something open source, php/mysql based if possible. I appreciate any responses...have been googling for two days and haven't found anything I really like.

Thanks...

TRAC is neat http://trac.edgewall.org/.

If you're looking for something helpful, and already put together. I would suggest assembla.com. I've used it for a few projects. Assembla is basically TRAC+SVN. Their accounts let you keep tickets on your projects, and apply time to each task. It will even tally all that up and do the metrics for you, with a burn-down chart and all.

I agree totally... My boss and his partner running another company both use it. They prefer it over ceberus, nagios, and all that other stuff that's out.