ClearCase was developed by Atria Software and first released in 1992 on Unix and later on Windows. Some of the Atria developers had worked on an earlier, similar system: "DSEE" (Domain Software Engineering Environment) from Apollo Computer. After Hewlett-Packard bought Apollo Computer in 1989, those developers left to form Atria. Atria later merged with Pure Software to form PureAtria. That firm was acquired by Rational Software, which was purchased by IBM in 2003. IBM continues to develop and market ClearCase. In September 2016, IBM announced a strategic partnership with HCL Technologies that will allow for accelerated development.