While there aren't any addons, you don't need any. Blender's game engine uses logic bricks, which includes a python controller for you to attach python scripts to any sensor input, or attaching a python controller to an always sensor will run your scripts repeatedly and the script can decide what input it responds to.
Python scripts can access any standard shared library function using ctypes. A python module can also be written using C/C++ as a large part of python already is, these binary modules can then be called from a python script. Note that the bge module that you use within any game engine script is already implemented using C/C++ code.
You may also be interested in cython, which turns a python module into C or C++ code that can then be compiled into a binary python module. It can be an easy way to get the python module support code that you then add your C/C++ code to.