I've been hanging out a lot on Less Wrong, which is a community for people trying learn about being more rational.
Some of us are also programmers... so we've decided to get together and have a hackday (in London). But we're still trying to figure out what would be both cool/interesting *and* help us build our rationality, *and* still be doable by an odd collection of random hackers over a single day.
But we need help coming up with ideas. Ideas that are not only small enough to fit into the time-schedule of a hackday... but that also demonstrably improve some aspect of our rationality.
If you have any ideas (or would be able to comment on those we've got), come over to our site and add our comments to the Designing serious games discussion.