People in the technical domain would know what Stack Overflow does. It is basically a Question-Answer Forum. There are many similar forums out there online. But what makes Stack Overflow stand apart from the rest is the quality and the uniqueness of the questions asked. Since it is a common practice in forums to find 2 questions which are kind of similar and questions whose answers are very elementary or can be found by a simple google search.
Stack Overflow gives credit to users who ask questions based on some research on the topic. And people who fail to do that are severely penalized. And at the same time for the guys answering the questions, standards are also given. If the answer does not solve the problem completely, people could downvote the answer. This makes StackOverflow great, where users constantly strive to achieve some kind of standard.
Most of the times when you pose a question of relevance you might get a response Immediately. But sometimes there are cases where you might have a good question, which does not get any response even after some days. Now for this StackOverflow has something called as Bounties. If the questioner does not get a response immediately, he could use some amount of his credit score and create a Bounty. And this question would be placed quite high in the list. There is an incentive for the person to answer the question since he not only gets credit for answering the question correctly but also gets the bonus Bounty Credits.