The design of RoboSim, a virtual environment for modular robots which controls simulated robots with code written for the hardware robots without modification, is described in detail in this paper along with its applications in educational environments. RoboSim integrates into the Ch programming environment, a C/C++ interpreter, that provides the ability to remotely control robots through interpreted C/C++ code allowing users to alternate between hardware and virtual robots without modifying the code. Open source software projects Open Dynamics Engine, OpenSceneGraph, and Qt are employed to produce the virtual environment and user interface which provide the capability of running on all major software platforms. The design of the software includes multiple library modules each specific to a particular task; therefore the simulation library and Graphical User Interface (GUI) can link against only the necessary libraries. The GUI links against the graphical library and XML library to give an interactive view of the RoboSim Scene as users are adding robots and obstacles into both the GUI and simulation. Execution of Ch code generates a new RoboSim Scene window which has the entire simulation that utilizes the simulation, graphical, xml, and callback libraries, in addition to the identical Scene from the GUI. It generates its own window for the user to view and interact with the progress of the simulation.