Virtual Programming is publishing Heir to the Throne (http://www.vpltd.com/index.php?main_page=product_info&products_id=253), the third expansion pack for Europa Universalis III. It costs US$19.95 and works with Mac OS X 10.5.8 or higher.
As its name implies, Heir to the Throne focuses on the diplomatic side of this strategy game, including the ability to establish dynasties of monarchs with arranged marriages that have far-reaching effects on history. In addition, it features a new Casus Belli system; peace treaties with more options; new options for the Holy Roman Empire, including reformations enacted via imperial authority; special diplomatic options for merchant republics, including trade leagues; a Cultural Tradition function that improves advisors the same way Military Tradition improves generals and admirals; and more.