[karmakaze]

Any number of casual indie mobile games would fit the bill. Pick a platform and come up with some simple game mechanic and backstory that seems like it would be fun. Just don't expect to make a lot of money or get only positive support, doing it for fun/learning and anything else is bonus is a good mindset.

I think the good thing about a mobile game is you can tell your friends (or anyone you meet) to find the game in the store and try it, right then and there. People often have bits of free time on their phone (when bored with the usual). On a computer, they'll be somewhere with many more obligations or distractions.