Ingress is an augmented reality GPS based mobile game.
It can be classified as Capture The Flag meets Hide-And-Go-Seek meets Risk meets GeoCaching.
Within the game world, certain objects and places have developed an energy called Exotic Matter (XM), seeping through portals or doorways from another dimension into ours. As most of these objects (sculptures, works of art, symbols, etc) and places (churches, universities, kingdom halls, etc) seem to be of an artistic or intellectual nature, it is assumed the energy is influencing the development of humanity.
The energy can be harnessed by finding these portals via a map-based scanner, hacking them to receive more energy and declaring for your Faction by installing harnessing devices called resonators. In addition to that, links can be set up between these declared portals in order to establish triangular fields that harness the energy and can thus influence more human minds.
The Intel Map, a map to track the various global portals, links and fields. Here you can clearly see fields established by the (green) Enlightened and the (blue) Resistance.
Within the story of the game two schools of thought developed: those who believe the energy needs to be harnessed for the good of all mankind, and those who fear the alien origins of the energy and wish to resist the 'Ingress' of the XM energy, the Enlightened and the Resistance respectively. Both battle to declare portals, deploy resonators and establish fields. Resonators on portals that have been declared by the opposite faction can be destroyed via weapons known as XMP Bursters.
a cross-faction meetup
The Ingress Scanner is a free software for iOS and Android developed by the Google startup Niantic. It is basically a Google map that via GPS can tell the location of the player and in relation to that show the various portals, resonators, links, fields and weapons, that otherwise are invisible in the real world.
The game is free but recently opened an in-app store to give players the ability to buy additional elements and tools, albeit they are in no way necessary for the game to be played. In addition to that Niantic has developed merchandise ranging from themed-phones to energy-drinks and of course the obligatory T-shirts.
The aim is to discover as many portals as possible, hack them, declare them, deploy resonators, destroy enemy resonators, establish links and fields. Each of these actions gather points and the more points, the higher the level of the player rises. It can be played locally and globally, meaning it is possible to establish links and fields that span the globe.
But all of this is only possible if the player moves physically close to the portals. Hence walking or cycling is encouraged and the game has thus been embraced by hikers and travelers. Using cars is discouraged as it can be distracting and the scanner can also register the movement speed of the player. Walking speed also gives points, while driving doesn't.
Once a player has chosen a Faction, they are contacted by other team players, usually via the in-game chat. While a single player can of course declare and hold/protect one or multiple portals, it is easier to declare them together and make them high-level portals with stronger defenses. As such Ingress is a team sport, and Factions meet for 'battles' over portals, fields and in-game elements.
Choosing the faction is often a moral choice, as it is never made quite clear whether the XM energy is good or bad. While it seems to be good, there are hints within the story of the game that the portals were opened by an alien race known as the Shapers. On the other hand, there is a human-made AI that seems to want to control the portals for its own nefarious uses, and so the two Factions are caught in the middle of the struggle.
This uncertainty is part of the expanded universe, which is explored in novels, comic books and various web shows, all of which style the game as not really being a game but an active and real struggle for world control. In fact, the actors in the web shows often make public appearances while remaining in character.
After a deal with Nintendo, Niantic was reported to be developing a new GPS game based on the Ingress engine, using the Pokemon concept.
Pokemon Go as such is set to become a game like Ingress, with Pokemons standing in for portals. A launch for the game has been set for 2016 on iOS and Android.