This cool little game lets you ride from Boston to Washington by answering questions about the Revolution. Its a combination of basic facts and some interesting trivia - like Benedict Arnold's leg - which makes the game more fun.
Yet it would be better still if you got more points for actually going and reading the For More Info links in each answer. Indeed, here's a perfect call for open-sourcing a learning app. A great base, with sound subject and content. So much more could be built on it:
So, PBS/TCPT, what about it? Emulate BBC; Creative Commons / open source your content?