Foamee, a site created by Dan Cederholm a few years ago is a perfect example of Reciprocity. The idea is quite simple: Someone does something kind or thoughtful for you, and you owe them a beer. It sits on top of Twitter’s API, and allows you to keep track of who you owe beers to and vice versa. It is a way to keep the promise of “Hey, thanks for your help. I owe you a beer!”. And what is better than than giving a beer in exchange for help from a friend.”

(via @regiskuckaertz)