Kelsey B. Plunking down her own cash made it feel like she had more skin in the game, while the promise of prize money at the end made it easier to treat herself along the way. I always thought of it as my money, so there was no monej of losing it. HealthyWage counts overusers since it launched inwhile the community-based weight-loss app DietBet has nearlyusers competing against friends or strangers. Still others, like Wellcoin and FitCoin, offer cryptocurrency or swag in exchange for healthy food and fitness choices. Some kinks are still being worked out in this market—one app shut down last year after the FTC found it owed users more than a million dollars, as Gizmodo reported in September. But the ones that are still around are as easy to join as buying a lottery ticket, and they competitiions scratch that same itch. If all participants succeed, everyone gets their money. Anyone who falls short? They have just donated to the cause. With HealthyWage, which Kelsey used, the stakes are...