7 tech revolutions that flopped

One of the stranger fads of the past decade was "check-ins." People would let the Internet know they arrived at a particular location, and that restaurant, or store would give them a deal in return.

Foursquare was the most popular check-in app, and many rivals popped up around it -- including Facebook (FB). But check-ins weren't driving business, and retailers eventually gave up on the deals.

In May, FourSquare gave up on the check-in part of its business, creating a new, separate check-in app called Swarm.