A collection of useful subroutines named the SpaceDyn is developed in order to offer an open, free tool of numerical simulations for researchers both in robotics and space engineering fields. The SpaceDyn is a MATLAB Toolbox for kinematic and dynamic analysis and simulation of articulated multibody systems with a moving base. Examples of such systems include a satellite with mechanical appendages, a free-flying space robot, a robotic system with structural flexibility, and a mobile robot, all of which makes motions in the environment with or without gravity.