Combine impulse buys with massive discounts and you get Groupon, a site that offers daily deals at restaurants, spas and other attractions in more than 90 cities in the U.S. and Canada. Groupon, which serves markets in 29 countries, teams with local businesses to provide one-day-only discounts; if enough people buy the coupon, it goes into effect, frequently cutting prices by half or even more. Groupon has spawned countless similar group-buying sites like LivingSocial, BuyWithMe and Yipit, to name a few, but none have Groupon's global reach. See Groupon's mobile app.