This book is quite good. I was recently looking for a more production-ready kalman filters, but the ones I found tend to be either abandoned, lacking lots of features, or not mature code bases. Are there any robust libraries for Kalman filters out there?
GTSAM [1] packs a lot of functionality for robotics projects, including Kalman filters [2]. A product of GTech (Frank Dellaert), a pro is there are many cool projects built on top of it [3], in C++ and Python. A con is GTSAM is not the cleanest, well-architected codebase (although far better than most products of academic labs).
The one quite often used in Robotics + ROS combination is robot_localization (https://github.com/cra-ros-pkg/robot_localization). The library provides implementation for ekf and ukf and in my experience it's quite robust.
SsfPack will still be faster though and be less memory hungry than Python. On the brief look I had, it also seems that the nonlinear/non-Gaussian simulation methods are not implemented.