Computing power and molecular simulation methodology have improved dramatically over the past decade, and for some systems molecular models are reaching a point where they can provide information that approaches or surpasses the quality of real experimental data. Molecular simulation can also be a potent tool for developing qualitative understanding, and this feature suggests widespread use of molecular simulation as a tool for teaching. Broader use of molecular simulation for these purposes requires tools that promote understanding and application of simulation software. We present an "object-oriented" view of molecular simulation that can help conceptualize and organize its elements, and discuss software development tools that we have constructed that enable non-experts in simulation or graphical programming to create instructive molecular simulations. We finish with an example of one such simulation applet, which we have used in the classroom. Tools described here are available on the web at www.ccr.buffalo.edu/etomica.