Mathematical Visualization Toolkit
MVT contains a scientific calculator, plotting tools, numerical tools, linear algebra tools, differential equations tools, content-specific applications, other Calculus visualization tools, and a tutorial-style help system.
Though the MVT contains a wide variety of tools for the visual learning for a variety of courses, it has the ability to numerically calculate and graph the solution to arbitrary differential equations with one, two, or three state variables, which makes this a potentially useful tool for instructors of differential equations. To use this part of the MVT, browse to Tools -> Graphing Tools -> ODE Integrator using the menu bar. The software is written in Java and so will run on a variety of platforms. It is distributed free of charge and can be launched from the browser or downloaded to the user's computer for offline access.
Link to MVT: http://amath.colorado.edu/java