According to a recent study conducted by Forrester Research, waiting in the checkout line is the top complaint among U.S. grocery, mass-merchandise, and convenience store shoppers. Mega-retailer Amazon and a quartet of well-funded retail technology startups -- Zippin, Standard Cognition, Grabango and Trigo -- believe they have the solution to the problem: Checkout-free stores powered by various technologies that enable shoppers to walk into the store, grab what they want off the shelves and just walk out. Autonomous checkout, another term for checkout-free, is becoming one of the hottest areas of retail investment today. It comes as the convenience expectations of today's Amazon-shopping, Grubhub-ordering, Uber-hailing consumers are ever-increasing, and informing their in-real-life (IRL) shopping demands. Brands are responding in kind, delivering digital services aimed at automating mundane tasks -- in this case, the checkout process -- so much so that the result is meant to feel "automagical," according to trend forecasting firm TrendWatching.