The Simile Project, of which timeline is just a part, is an MIT initiative aimed at developing and promoting semantic web technologies. The project is well documented and open source. The presentation and functionality are easily configured and the timeline will display a wide range of common data formats including, XML, RSS, Atom and iCal. To see this in action check out the Universal Timeline Aggregator.
The Simile timeline uses an innovative solution to the problem of navigating long or highly detailed data. The user is presented with a series of bands stacked one atop the other. Each band represents the same timeline at a different scale. What is really interesting is that you can synchronise the bands so that dragging one band will correctly reposition all the others.