This is their original game created back in 2012 on Android and 2014 for iOS. There are two sides: Enlightened (green) and Resistance (blue). There is some back story about saving the world that everyone ignores. Essentially places of interest are called portals. These might be a statue, church, park bench, whatever. If it is uncaptured then a player can deploy resonators upon it and own it. They can protect it with mods such as shields, and they can link it to other portals.
If a player comes across a portal owned by the other side then they can battle using Bursters and other weapons to defeat and own the portal themselves. A portal can be recharged remotely (but this rarely stops the inevitable win from the player on site).
In order to make a link between one portal and another, the player must possess a key for it. These can be collected when visiting the portal, and can be picked up after a link is broken or dropped for collection by another player.
When a player links 3 portals together to make a triangle then this is called a field. A field covers an amount of the human population which approximately determines the size of the field. The side with the largest number of population covered is winning.
The picture above shows the Statue is a portal, and that it is owned by Resistance (blues). The portal is linked to other portals nearby and this makes a field. Ingress does not use Augmented Reality.
More information can be found at: https://www.ingress.com/
The website also contains a map of every portal, link and field at: https://www.ingress.com/intel
Ingress requires significant co-operation between players of the same side in order to co-ordinate the location of keys and is therefore a highly social game for many players. The demographic for this in my unresearched opinion is 25+. The game certainly started as predominately male but is better for an significant increase in females now. Google Hangouts is often used to co-ordinate strategy while the Intel map is essential for seeing what is happening in real time. This is global game with millions of players, many of whom submitted the portals that made Pokemon Go possible.