Do you know Simbody?

https://simtk.org/home/simbody/

You can check this overview site for a more or less comprehensive list:

http://real.uwaterloo.ca/~mbody/#Software

some of the software listed there is open-source.

We have developed an Open Source Multibody Dynamics simulation code:

http://www.hotint.org

There is lots of Documentation and you can also use this as a Windows executable.

these are the packages I have found so far:

Darwin2K

Gazebo

simrobot

opensim

ODE Open Dynamic Engine: http://ode-wiki.org/wiki/index.php?title=Main_Page

Orocos

OpenRAVE

bullet: http://bulletphysics.org/wordpress/

DANCE: http://www.arishapiro.com/dance/

dVC3d: http://www.cs.rpi.edu/twiki/view/RoboticsWeb/DVC3d

IBDS: http://www.interactive-graphics.de/

MBSim

Moby : http://physsim.sourceforge.net/index.html

RBDL, the Rigid Body Dynamics Library: http://rbdl.bitbucket.org/

Siconos Platform: http://siconos.gforge.inria.fr/

SOFA: https://www.sofa-framework.org/

Solfec: https://code.google.com/archive/p/solfec/

PROJECT CHRONO: https://projectchrono.org/

MBDyn: https://www.mbdyn.org/

HOTINT: http://www.hotint.org/

Simbody: https://simtk.org/home/simbody/

AR-CAD: http://www.ar-cad.com/index.html

v-rep coppeliarobotics.com

Linkage http://blog.rectorsquid.com/

OpenHRP3

 Thank you Eric ... 

Hello, I develop the opensource software openmeca : https://gitlab.com/damien.andre/openmeca available for Windows, Mac OsX and Linux. OpenMeca is a standalone program designed for educational mechanics. OpenMeca does not support cosimulation. Its usage is very easy but it does not gives realistic drawing of system because openmeca uses symbols instead of real parts with complex geometries.    Some examples are available on youtube.

 Thanks, Damien. Looks cool !!!

You are welcome ! :)

if you use it, don't hesitate to give me your feedback to improve the soft.

Check the notes section of www.concurrent-dynamics.com. The down-loadable pdf’s shows how to formulate the eom efficiently for generic multibody simulations, to simulate it and to test it. All for free! Enjoy the pdf’s.