DynaSys can solve first order systems of ordinary differential equations. It can solve both initial and boundary value problems for differential equations. It offers a variety of numerical methods for solving the equations. It can display the results graphically in phase-portraits, plots of independent vs. dependent variables, or 3-d plots. In addition, it can compute function iterations and display the results in stair-step diagrams, or as simple plots of the points of the iteration. All plots of solutions may be moved and their sizes may be changed. Text may be interspersed with plots. The basic concept in DynaSys is to put a piece of paper on the computer screen, on which you may draw as many different related plots of solutions as you desire, in any arrangement, of any size. DynaSys originated in the desire to have an easy tool to create useful graphics to distribute to students in a differential equations course, but it has gone far beyond that now. It is distributed freely over the Internet from the IDEA site. This project has been supported in part by the National Science Foundation, and by International Thompson Publishing, through its Brooks-Cole Division.