Hackathons are volunteer-driven technology building gatherings usually between 30 to 200 strangers gathering around a certain technology or social problem. Teams form around project ideas, and build them in a day or so. It's a race against the clock to find an idea, make prototype and to demonstrate it at the end of the event. There's usually a judging panel who award a prize.
This is a companion discussion topic for the original entry at https://peerlearning.is/farmhack-small-group-projects/