Wikipedia
OpenStudio is a suite of free and open source software applications for building energy analysis used in building information modeling. OpenStudio applications run on Microsoft Windows, Macintosh, and Linux platforms. Its primary application is a plugin for SketchUp, that enables engineers to view and edit 3D models for EnergyPlus simulation software.
OpenStudio was first released in April 2008 by the National Renewable Energy Laboratory, a part of the U.S. Department of Energy. NREL reports an average of 700 OpenStudio downloads per month. Google's strategist for SketchUp, remarked that "OpenStudio is lauded around our office as one of the most complicated plug-ins ever written for SketchUp".
OpenStudio was designed to work with SketchUp, because many architects already use SketchUp for building designs. The integration allows architects to analyze a design's energy performance before beginning construction.
The first private organization selected by NREL to conduct OpenStudio courses was Performance Systems Development, a New York-based training institute. Courses will be conducted for building professionals, software developers, and utility administrators.