Atria Software
Atria Software Inc. was a software company that developed ClearCase in the early 1990s. It was founded by David B Leblang, Paul Levine, David Jabs and others on January 11, 1990. 
Some of the Atria developers had worked on an earlier system: DSEE (Domain Software Engineering Environment) from Apollo Computer. After Hewlett-Packard bought Apollo Computer in 1989, they left to form Atria.
Atria later merged with Pure Software to form Pure Atria. That firm merged with Rational Software, which was purchased by
IBM in 2003. IBM continues to develop and market ClearCase.

References

Software companies based in Massachusetts
Defunct software companies of the United States