TempleOS is a biblical-themed lightweight operating system (OS) designed to be the Third Temple prophesied in the Bible. It was created by American programmer Terry A. Davis, who developed it alone over the course of a decade after a series of manic episodes that he later described as a revelation from God.

Terrence Andrew Davis, better known as Terry A. Davis, was an American electrical engineer and computer programmer best known for creating and designing TempleOS, an operating system in the public domain. Its development was an extremely complex, time-consuming, and unusual undertaking for one person.