This paper introduces I-GMS, a dynamic simulator that accommodates various systems of rigid bodies, ranging from a single free flying rigid object to complex linkages such as those needed for robotic systems or human body simulation. I-GMS's object-oriented design provides a generic framework for representing various types of rigid body systems, and exploits virtual functions to apply common kinematic and dynamic functionalities to them. Moreover, I-GMS supports interactive simulation so that it easily incorporates user-input for the on-line editing and modification of trajectories. User-interaction is achieved with the PHANToM haptic device, which runs as an integrated part of I-GMS. We demonstrate I-GMS's capability to simulate general multi-rigid-body systems through examples that include a free-falling sphere, a robot manipulator, and a human body model with 36 degrees of freedom (dof). We present a simple example of interactive simulation for a 3-dof-robot manipulator.