Similar to ARKit, ARCore finds flat surfaces where virtual objects could be placed. It is aware of lighting and includes orientation abilities and spatial awareness. This means you could, for example, place an object on a table and then proceed to walk around it to take a 3D vantage point of the virtual object. ARCore works in line with the Unreal and Unity engines in addition to JAVA/OpenGL.
Apple's ARKit utilizes Unity and Unreal too but uses frameworks such as Metal and SceneKit which are primarily developed by Apple. Augmented reality may be the next big frontier for mobile technology, but Apple won't necessarily be dominating the field.
The industry knows that the audience and profits inherent in AR are too vast.
To confront this, Google has offered up a preview of its new ARCore, which is Google's answer to Apple's ARKit.