To motivate them to participate in open source projects and communities, such as StackOverflow…. Let’s face, most (I mean 99.9%) of developers already used StackOverflow to unblock some stuff…. And, unless that you belong to the 0.1% of programmers that never used an open source library , you’ve used some type of open source in your projects…. And how many have contributed back? I don’t know, but the point is that these guys that contribute back are good developers, they care about the craft and they help people. Would that be nice to have a team with this type of mindset?
I bet it would. I bet it would bring a lot more value to final product, than just a team of stackoverflow consumer developers. So, why not motivate your developers to choose a topic, and start being a subject matter in Stackoverflow or any other forum? Or motivate them to choose some open source library/project and contribute to it?