Google Play's games services differs from Apple's Game Center in that it offers backend support, rather than a standalone application.
Anyone making a game with Google Play has access to its developer services. A handful of games already have these services incorporated: World of Goo, Super Stickman Golf 2, Beach Buggy Blitz, Kingdom Rush, Eternity Warriors 2 and Osmos.
"We won't make it a mandatory exercise, or have any certification process around it," Google lead product manager Greg Hartrell told Engadget. "We create fantastic services that allow developers to create these great game experiences, and help promote their discovery, help retain their users and keep them engaged."
Check out the games services on Google's developer site.