The Princes' Kingdom is an adaptation of Vincent Baker's Dogs In The Vineyard. It has a very different slant, however. It's designed for play with children. As such, it takes out a lot of the more adult content of Dogs (e.g. sex and theology) and replaces it with a fairy-tale setting.
The characters are young (ages 5-12) princes and princesses in a fantasy kingdom, Islandia. They have been sent out on a boat by the King to travel from island to island in the kingdom, to prove whether they will be fit to rule when they are older.
The island creation section is simple and brings into focus issues of government, law and order, and colonialism or diversity. However, the basic idea is the same as in Dogs - the GM creates a bad situation and the player characters have to decide what's wrong and sort it out.
The text and mechanics are simpler than Dogs, clearly to make it more accessible to younger readers. This doesn't look like it will detract from play one bit. And adults will find this fun too, even if it is designed for play with adults and children (family play, really).
Now I just need to wait for my daughter to be old enough to try it...