ODE Softare
For those of us who don't have the Grapher app that comes on Macs, this is a great substitute. You can create direction/ vector field graphs or phase plane graphs, using the differential equation you type in. (Note: as you are typing in the ODE, the application will probably tell you that you've made an error, but the error message goes away once you've finished typing. Page takes a while to load. Available as MATLAB m-file or as java applets.

ODE Software .