The way it works is that Groupon negotiates a steep discount -- generally about 50% off -- with a local merchant. But to get the deal, a certain number of people have to "buy in."
Groupon = group +coupon.
I belong to Groupon.com in Los Angeles and have seen discounts for spas, restaurants, events, and even ferry rides. Some of the discounts seem like great deals to me, others are so so. It really depends on how you spend your money. Groupon also features deals for theater tickets, classes, bars, museums and gyms.
Check if Groupon.com is in a city near you.