Related packages
Here’s a list of some related packages. None provide the same functionality as npsolve, but they might be useful for you.
Scipy (Just use the solvers directly)
Odespy (Class-based models possible, but it looks bit less flexible.)
Pymunk (2D rigid body motion)
PyDy (Based on symbolic equations)
Hamilton (not much documentation?)
Arboris (robotics)
Sympy mechanics (a great package, and somewhat object-oriented, but since it is symbolic, it will struggle with discontinuities.)
PyODE (possibly dead?)
Odelab (Class-based to some degree, but it looks less flexible.)
Pyndamics (ODE wrapper)
ARS (Robotics)