AndoSim
AndoSim puts the cubic barrier contact method from a 2024 paper inside Blender, so cloth and shell contacts can be simulated and looked at in the scene.
Independent implementation and Blender integration. Based on published research and the PPF contact solver.
There's a C++ core with Eigen and pybind11. The Blender layer exposes pin constraints, contact settings and debug overlays, and the Python side passes scene data in and brings state back out, which is where most of the fiddly work sat.
There are numerical derivative tests and packaged releases next to the demos, though that testing covers the checks and doesn't go much further. The method and the optional PPF backend belong to their authors.
State
A released add-on with a native solver, bindings and test scenes. The integration is mine.