MBDM is a set of MATLAB functions that can be used to construct and solve a multi-body problem of general complexity. The assumptions of the code are that bodies are rigid, and joints are frictionless. More about the code and its usage can be found on https://www.windflow.pl/project/MBD
Documentation is in form of compiled pdf file. It covers definition of bodies and joints, and basic derivation of all equations.
Although the code is usable, it is rather a proof of concept. More sophisticated and way faster version was written in C.