Dear OpenSim user, OpenSim version 1.9.1 is now available for download. OpenSim is freely available to the biomechanics research community and enables modeling and simulation of human and animal movement, including inverse dynamics analysis and forward dynamic simulation. The new version allows viewing, and transforming marker trajectories and ground reaction forces obtained from a motion capture system. It also adds a new analysis to compute Joint Reactions throughout a motion. The software, models, tutorials, and example simulations are available at the project website: https://simtk.org/home/opensim. Best regards, -Ayman Habib On behalf of Scott Delp and the OpenSim team.