Project info: WikiTimeline
Technology: HTML, PHP
License: Closed source, personal
Although the source code for this project is not freely available it is an open source initiative. Like all Wikis it relies on the support of a community to enter and maintain the database of historical information. So far the contributors have produced 170 timelines and given the volume of information required to populate a project like this I think an 'open data' policy is a very pragmatic approach.
I'm not crazy about the design (a little too 'web 2.0' for me) but I do like the idea of giving each category it's own timeline layer. This allows users to explore and discover concurrent events across categories.
This notion of exploration and discovery is going to be key to making the user experience rewarding. The interface should encourage playful exploration. It's absolutely what makes Google Earth fun to use.