MBDyn is described as 'is the first and possibly the only free* general purpose Multibody Dynamics analysis software, released under GNU's GPL 2.1 (get a cached copy here)'. There are eight alternatives to MBDyn for Windows and Linux. The best alternative is CarSim. It's not free, so if you're looking for a free alternative, you could try QuickField or RoboAnalizer. Other great apps like MBDyn are RecurDyn (Paid), mbsim-env (Free, Open Source), SIMPACK (Paid) and MADYMO (Paid).
RoboAnalyzer is a 3D model based software that can be used to teach and learn the Robotics concepts. It is an evolving product developed in Mechatronics Lab, Department of Mechanical Engineering at IIT Delhi, New Delhi, India, under the guidance of Prof. S.K.
RecurDyn is Computer Aided Engineering (CAE) software that is focused on Multibody Dynamics (MBD), while offering multiphysics solutions. The technology behind RecurDyn has superior calculation efficiency because it is based on recursive formulation.
LMS Virtual.Lab is an integrated suite of 3D FE and multi body modeling software which simulates and optimizes the performance of mechanical systems for structural integrity, noise and vibration, system dynamics and durability. Using LMS Virtual.