Google's popular Android-centric "turf war" game, Ingress, has finally lost its invitation-only requirement and has entered open beta. Starting today, all Android users can download the massively-multiplayer game from Google Play for free.

Developed by a Google subsidiary called Niantic, Ingress is an augmented reality game set in an alternative version of the real world. Players take a side -- Enlightened or Resistance -- which battle against each other over "Exotic Matter" (or XM), which is seeded throughout actual locations around the world. Gameplay involves taking control of "portals," which are typically placed in conjunction with the location of popular real-world landmarks such as sculptures, libraries, churches, and other heavily-trafficked buildings. The bigger the city, the more portals it tends to have, with densely populated areas the most portal-rich parts of the game map. Additional portals are added to the game as users -- now located in 200 countries -- continue to sign up.

Naturally, the game mechanics involve significant complexity beyond this basic setup, but the key is that Ingress involves physically traveling in the real world to capture territories and collect virtual objects to score points and advance in the game.

In closed beta for about a year, Ingress has already chalked up over 1 million downloads. The game will transition from the current open beta to its official public launch on December 14 as the story begins to heat up.

In sync with its transition to open beta, Ingress is heating up its plotline by giving Enlightened and Resistance players a specific goal. (Enlightened players have to complete a certain project, Resistance players have to stop it.) It's the next big step along a long-arc narrative that will be reaching its climax, Google says, in about 24 months, when the story reaches its "satisfying conclusion." A sequel or spin-off hasn't been ruled out.

In conjunction with today's open beta launch, Google is also offering its top players over the next month a chance to win a trip to Google headquarters where they'll get a chance to collaborate on future developments in the Ingress storyline. Those hopeful for the win will also need to make their case via a "creative" social media post.

Ingress is compatible with a wide range of Android devices running Android version 2.3 and up, with especially smooth performance on devices optimized for heavy graphics and complex gameplay, including Qualcomm Snapdragon-powered smartphones and tablets.

This story, "Google's augmented reality game Ingress opens to everyone" was originally published by BrandPost .