Mobile check-in app Foursquare launched a feature called Explore last year. Explore uses algorithms to suggest restaurants and places to visit nearby based on the check-in history of that specific user and his or her friends. Today Foursquare is launching a recommendation engine for the web.

Mobile check-in location service Foursquare has hit 15 million users, which is triple the number of users they had during this same time last year. Half of their users are in the U.S. and the other 50% is international. Now that Gowalla has been acquired and will be rolled into Facebook, Foursquare will have even less competition.

Foursquare APIs are used for applications such as Instagram, Thrillist, Localmind, Foodspotting, GoSocial by American Express, Quora, The Conan Blimp, and LocaModa. Since Foursquare’s developer community is growing, the company unveiled a newly redesigned developer website at developer.foursquare.com. Foursquare launched developer.foursquare.com in December 2010 along with the newest version of their API. Foursquare added new platform features such as Venue Project and Realtime Push APIs. Foursquare also retooled their Getting Started Guide. This should make life easier for Foursquare developers. [Foursquare Blog]

Foursquare has added Radar as a feature to their mobile app. If you follow a list or if you have a place on your to-do list that is near-by, then Radar will notify you about it as a reminder. Foursquare’s Radar feature works on iOS 5.

Geolocation application company Foursquare has hit one billion check-ins. The application went from 100 million check-ins in July 2010 to 200 million in October 2010. Then they hit 750 million check-ins in June 2011. Foursquare has launched a new version of the app. Now it has a tab for its new Lists feature. Check out the video below:

Foursquare has been rolling out a bundle of new updates this month, from inline photos and tip lists to redesigned apps, and is now introducing yet another new feature: events. Users previously could only check in at places, but Foursquare is now adding major events to their database. They gave events a test-run during SXSW conferences and are now partnered with ESPN, MovieTickets.com and Songkick. The partnerships mean that when users go to check in on Foursquare, they’ll see official pages to check in at sports events, movies and concerts.

Foursquare has two big announcements: the first is a site feature called Tip Lists. The second is that United States President Barack Obama has joined geosocial network Foursquare, checking in at presidential events as he tours the country. The White House blog says the President’s Foursquare profile will feature tips with “the places President Obama has visited, what he did there, plus historical information and more.” The account already has more than 12,000 followers. Mashable theorizes that this may be a watershed moment for Foursquare as people join the network to follow the President’s travels.

Redbox and Foursquare have teamed up to run a promotion from August 15th to August 24th that will offer discounts to customers who check in to a Redbox kiosk on Foursquare. The dvd rental company has apps for iPhone and Android that provide users with info like Redbox locations and which titles are currently available where. Mashable reports that the check-ins will get customers discounts between ten cents and a dollar.