I've got a project that I'm working on that could really benefit from that free time. But like most HNers my project isn't going to change the world - but it's

I've got a project that I'm working on that could really benefit from that free time. But like most HNers my project isn't going to change the world - but it's an interesting technical challenge. If I had 6 months of free time I'd like to make something that could potentially do a lot of good. For example, an app that gamifies doing nice things for other people.