The premise of Upside is simple enough: Reward business travelers with gift cards for being a little more flexible with their flight and hotel. Pulling this off is a bit more complicated. “When Priceline was created, we knew that flexibility would become an extraordinary asset in the modern commercial world,” Walker told Fortune in an interview. “We also knew that to really make it work you needed enormous software power and you needed all kinds of tools that didn’t yet exist. Get the full story at Fortune