OpenSim Creator is open-source software for creating/modifying OpenSim models, available at https://opensimcreator.com
It's a UI that has tooling for:
- Editing model properties
- Visually inspecting the model
- Plotting/tweaking model parameters, with live updates
- Specialized tasks, such as importing and warping meshes
Available from https://opensimcreator.com, or its GitHub repository (https://github.com/ComputationalBiomechanicsLab/opensim-creator).