Originally Posted by gmw
This sounds a lot like what I was looking for (but Windows friendly) in an earlier thread. I found nothing very good I'm afraid (to the point of making some tentative designs to write it myself). I especially can't help you with free and Mac friendly, but you may like to look at project management software (you know, the stuff they use for planning road works etc), that's where I was going to look when I next had time.
Visio has a great time line tool in it. It's a chart with notations. You determine the beginning and ending points by dates (change as needed) and click and drag a box to the date on the line you want, then add notes inside the box. It's used quite a bit in construction litigation.