The Google Thread IoT protocol is an open source technology, based on physical and medium access control layers specified on IEEE 802.15.4 (like ZigBee, among other protocols), with a link layer addition from IETF, 6LowPAN. This composition makes the Google Thread routable in IPv6. It is a combination of 6LowPAN, IPv6 and UDP as the transport layer, which are all protocols specified by the IETF, seasoned with robust security and commissioning additions from the Thread Group. This makes Google Thread a sure bet in the IoT industry.
Thread was originally conceived as a consortium of companies (the Thread Group alliance) that built the standard and associated certification programs. Now, as one of the main drivers of the alliance, Google Nest has released a complete open source version of Thread (release 1.1.1) as Openthread project, which is available on Github since July 2017. That has created a considerable buzz in the IoT scene, as it is difficult to find flaws in the overall concept based on its components. Thread is open source and available to whomever wants to develop devices and applications.
The main use-cases for Google Thread would be for smart homes and similar applications. Thread is expected to compete closely with ZigBee, as it shares the same physical and medium access control protocols.