Ingress has been in closed beta for quite a long time, and the beta has grown considerably. Right now, Ingress is in the 1 million to 5 million download range in the Google Play Store, which is quite a sizable beta. But, Google and Niantic are finally ready to open up the MMO game to everyone, which means you no longer need to have an invite to get in on the fun...Source: http://www.phonearena.com/news/Ingress-leaves-beta-now-available-for-everyone_id48933
