Swappi uses a view-and-swipe interface to match one swapper with another. It's a little like Tinder, but for second-hand items like mobile phones, electronics, games, books or even cars.
You start by posting a photo and a value on Swappi. Then the app shows you pictures of items that other users are offering to trade. Swipe right if you're not interested, swipe left if you are. When users make a match, they open a chat window and close the deal.
Unlike classified ads, you don't have to know what you want and search for it. And, unlike an auction site, there's no money involved and no commission to pay.
Swappi is free and available for iOS devices at the Apple iTunes App Store.