Groupon, launched in November 2008 in Chicago, is a highly successful online marketing venue for businesses looking to gain more customers and for consumers looking for great deals on things they already buy. Here’s how it works: Businesses wanting to reach more customers sign up for a “daily deal” promotion where they offer some product or service at half off the normal costs. Groupon then sends that offer out to a list of users who have signed up to receive these daily deals. But here’s the “catch” (or the brilliance depending on how you look at it): in order for the deal to be “on,” a certain number of people must buy the deal – otherwise it’s off.