Foursquare is an application for smartphones that allows you to register the places you have been. It is also a social network , meaning your friends can see this information.
You can also discover cool places that people are visiting: pizzerias, museums, shops, etc.
And if you have a business and would like people to book when they are there. Just register and disclose.
I selected a video tutorial that teaches you how to register your company on Foursquare . And the best: it's free !
Oh, and the Foursquare link: www.foursquare.com