Because NREL no longer prominently features legacy releases on the front page, finding and installing 2.9.1 requires a direct link to the GitHub releases page.
This report was compiled from official OpenStudio GitHub release notes, NREL documentation, and user community feedback from the 2019–2020 period. openstudio 2.9.1
If you are maintaining older models or need to reinstall this specific version, these details are critical: Because NREL no longer prominently features legacy releases