  The rapid growth of the world's population demands more natural resources,
food, and space. World-renowned physicist Stephan Hawking has argued that soon
we will require another world to live on because we are running out of space
and natural resources. This ever-increasing demand for resources and space
needs novel technologies to explore natural resources, produce more crops, and
explore outer space. Internet of X-things (X-IoT) is an enabling technology to
overcome all of the above issues. In this article, we have presented an
overview of a unified framework of X-IoT. The framework of X-IoT consists of
three major categories. The first one is the Internet of underwater things
(IoUT) for smart oceans. The second category is the Internet of underground
things (IoUGT) for smart agriculture, seismic monitoring, and Oil/Gas fields.
The third category is the Internet of space things (IoST) for outer space
exploration, to provide global coverage, and to enable inter-satellite
communications. Through this framework, we get to know what has been done since
recently and how the technical challenges across the broad spectrum of emerging
use cases under the water, underground and over the space are converging toward
future solutions.
