I’ve been looking at Ancestris, a free (GPL’d) genealogy program written in Java. It runs on Windows, Macintosh, and Linux systems.
There is very little documentation with the program and it takes a bit of working with to figure out some of the features included. For instance, when I ran the GEDCOM compliance checks it came out with a categorized list of items in one pane and a linked editor in another pane.
There are three editor panes to choose from. One fairly simple, one fairly complex, and one for directly editing the GEDCOM.
The GEDCOM check feature goes beyond just compliance with the standard and includes some plain old sanity checks. Some of these checks are for settable values and ranges so you can tighten or loosen them at will.
The general reporting capabilities are lacking, compared to other free and commercial genealogy programs. There is only the option to output to a website, for instance. The styling of the report is fairly simple.
Ancestris is available on the web at http://www.ancestris.org. It is updated often as it is a work in progress.