Brainware
Founded by Bryan Amoot, Brainware is a developer that started off making level editors, but currently create apps for iOS.
The company was originally contracted to create level editors for Interplay's titles, and released two Descent level editors - Descent Mission Builder, which saw an commercial release, and Descent Mission Builder II, which was bundled with Descent 2's expansion pack and later Descent compilations.
They also created level editors for Star Trek: Klingon Academy and Forsaken, but neither were released, as Forsaken didn't meet sales expectations and Interplay decided not to ship an editor with Klingon Academy.