Has anyone heard of any FOSS research software for chronological analysis of dates and events in history? The idea would be that you input events into a database, along with known dates, and known time relation of certain events to other events, and the software calculates and displays some kind of timeline based on your calendar type and other settings.

I study ancient history and am interested in developing my own chronology of how events happened in the past, and I am looking for a relevant FOSS research tool. Often times from ancient history we don't know an exact date of when something happened, but rather how it relates to some other event (e.g., happened in the third year of the king of so and so...). So the ideal tool would allow you to make some small changes in the data and see how it affects your overall system.

If no such FOSS software exists, I might be willing to code some myself. So I'd also appreciate any relevant information, such as libraries that might possibly useful, and similar programs in the proprietary software world which could serve as an example for features, approach, and so forth. Even aborted projects (started, but never completed) might be interesting.

The main thing would be to specify a XML subset for the purpose.
Then your goals can be broader.

There is this gnowledge project: gnowledge.org
It should be easily adaptable for your purpose.