Google last talked at length about their Nearby API (application programming interface) at IO 2017, where its mission statement was detailed. Fast, encrypted, offline, peer-to-peer communication is Nearby's goal, and today Google opens up the doors for developers to integrate the latest version into their apps.
Nearby uses a combination of Wi-Fi, Bluetooth LE, and regular Bluetooth to discover and connect to devices that are, well, nearby. Although the Wi-Fi chip is being used, a connection to Wi-Fi or any form of cellular data is not necessary, facilitating users to transfer or stream data to or from their devices, when no network is available. By utilizing the best parts of these communication standards, Nearby is able to create high-bandwidth, reliable, and encrypted communications, while sidestepping many of the ills of any one of these standards, like poor connection, or fluctuating speeds.
Think of it like NFC on steroids, where only proximity is needed rather than a tap, and the amount and size of data is essentially limitless. Such use cases could include sending a message to those in a subway station to inform them of delays, media hubs from which people can stream music or movies to their device, or simply for creating a chat hub at a public venue - all without touching the internet.
In fact, similar implementations are already being built. The Weather Channel is implementing Nearby in its app to help spread urgent weather warnings to those in data-deficient areas, while Hotstar is enabling the ability to share media from its app without an internet connection, and GameInsight is using the technology to run entire games offline.
Unfortunately, the Nearby-powered private driveway/parking spot renting app Google spoke of at I/O has yet to be created. We'll be waiting for that one with baited breath, Google.
source: Android Developers Blog