The issue tracker item reveals the phone will feature a a standard 4MP colour backside camera, a 180 degrees Field of View (FOV) Fisheye camera, a depth camera 320x180@5Hz and a front camera with a 120 degree FOV. The latter should have the same field of view as the human eye.
Project Tango is a project by Google’s Advanced Technology and Projects group (ATAP). The project aims to make it possible to create a 3D model of the space around the phone. It is e.g. able to create a 3D map of your home, simply by walking around.
This way it's possible to create indoor 3D maps to make it easy to navigate through buildings like offices and supermarkets. It can also be used to make e.g. 3D maps of your own home for usage in games as Google states on its website: "imagine playing hide-and-seek in your house with your favorite game character, or transforming the hallways into a tree-lined path. Imagine competing against a friend for control over territories in your home with your own miniature army, or hiding secret virtual treasures in physical places around the world."
To make it possible, Google has a prototype 5" Android phone ready. This contains customized hardware and software designed to track the full 3D motion of the device, while simultaneously creating a map of the environment. These sensors allow the phone to make over a quarter million 3D measurements every second, updating its position and orientation in real-time, combining that data into a single 3D model of the space around you.
Google will make the first prototype phones available to developers today. So far the company has not disclosed when the technology becomes available in commercially available phones.