In April of last year, shortly after Apple announced its Game Center social gaming platform, the Japanese company GREE purchased the social gaming platform OpenFeint for $104 million.

Not having done much with the service since the purchase, it soon became apparent that the purchase was more of a bid to convert OpenFeint users (and developers) over to GREE’s own social platform. Despite assurances that OpenFeint would be supported into 2013, GREE recently announced that it will be shutting down OpenFeint on December 14th, a decision which caught many in the development community by surprise.

The main benefit that OpenFeint had over Apple’s Game Center was that it supported cross-platform challenges, leaderboards, etc. between iOS and Android games. The loss of OpenFeint means that developers upset with GREE and/or who are unwilling to convert to GREE’s own platform will be left stranded when it comes to their Global leaderboards.

That’s where Heyzap comes in.

Today Heyzap unveiled the addition of Social Leaderboards to their cross-platform SDK allowing users to “challenge their friends to beat their scores and see what position they score against their friends”, no matter if the fall into the iOS or Android camp. “In addition, the challenge mechanic sends a real-time notification to the other player, engaging them to play you back.”

You do not need to have the Heyzap app installed in order to receive the notifications, however you must have it installed to see the full leaderboard and have the full functionality.

These global leaderboards are just the latest addition to Heyzap’s already nice social features which includes social sharing via Facebook and Twitter and a Foursquare like check-in system where you can attempt to be the ‘Boss’ of an app by checking into it the most often. Their website lists ‘Achievements’ as a forthcoming feature as well.

“Along with the check-in SDK, which allows users to easily promote which games they are playing, Heyzap is now connected to over 3,000 games on Android and iOS”. There are currently over 50 games already integrated with Heyzap’s new SDK. Now they are opening up the new leaderboard functionality to all game developers.

If you are a Developer looking for cross-platform leaderboards you may want to check out Heyzap, which (according to their website) can be integrated in 15 minutes, with just a few lines of code and about an extra 100KB added to your file size. Heyzap is even willing to QA the integration for you.

Developers can download the free leaderboard SDK from Heyzap’s Developer Portal.