Facebook Places lets people share their location with friends, see who else is in the area, and explore new places by monitoring locations where their friends have “checked in.”

For more information and to start using it today:

Foursquare is a mobile application that makes cities easier to use and more interesting to explore.

It is a friend-finder, a social city guide and a game that challenges users to experience new things, and rewards them for doing so.

Foursquare lets users "check in" to a place when they're there, tell friends where they are and track the history of where they've been and who they've been there with.

For more information and to start using it today: