Expanding on the premise that most activities – including shopping and work – aren't as stressful if they feel like fun, gamification has risen to prominence in the world of retail. Merchants as diverse as Nike, Whole Foods and New York-area drug store chain Duane Reade are taking a long, hard look at how online games and apps can help them improve the bottom line while keeping customers -- and employees – entertained. And, the retailers hope, loyal.