Having some kind of family tree software could be handy in Pendragon. Until someone develops an app personalised for Pendragon, there are some programs out there worth a look.
I haven't reviewed them all, I present these links as is- maybe someone will test them out and find out which is best:
(Feel free to use this thread to post links to similar programs, or comments on those below.)

GRAMPS: http://gramps-project.org/features/ (Open source)
Personal Ancestry File: http://www.familysearch.org/eng/paf/
Ahenblatt: http://www.ahnenblatt.com/
Legacy Family Tree: http://www.legacyfamilytree.com/

There are programs that allow you to create collaborative websites, so that for instance, the players in yoru campaign can individually update their family data and it is visible to all. I haven't explored them, but found one interetsing wiki:
Wikitree: http://wikitree.org/ allows you to create tree-based pages, handy for family trees. Might get complicated for multiple marriages, etc., which dedicated genealogy software should cope with.