One of my favorite new apps that use the Foursquare API is Fourstalgia. It’s a very cool hack project built by Jon Hoffman @hoffrocket, an engineer at
I love this concept, but like many applications, it appears to be mostly focused on the USA and Europe. I live in New Zealand and whilst there are amazing historic photo libraries here, they are not available on the service which this app uses, so I guess I won’t be installing it. It was worthy of mention. If you live somewhere that is supported with historic images, I would recommend trying this out.