Ingress is an Altered Reality Game (ARG) from Google, specifically a company called Ninantic. They are some how related to the Google Maps people.
The app is basically a form of Google maps, with the colors shifted to darker colors.
The purpose of the game is to control Portals, link those portals and create fields with three links.
Two factions compete for those, the blue Resistance and green Enlightened.
Portals exist all over the world. Historic sites, libraries, interesting man-made feature, religious buildings, statutes, local meeting places... All could be portals. Most are actually user submitted too. With more being added all the time.
Here's there marketing video, https://youtu.be/92rYjlxqypM
It's a game that gets you out of the house, as you have to physically visit these places.
There's a bunch of local coordination done via Google hangouts and G+. It is Google's game

Anyone can download the app (it used to be invite only when it started a couple years ago), but there is an in game badge/achievement for inviting people.
If you are interested, I can shoot you an invite or explain more here.
I played last year but stopped for a bit. Boring infernoless day for me installing it again.