DFIELD and PPLANE programs are described in detail in Ordinary Differential Equations using MATLAB by John C. Polking, Department of Mathematics, Rice University. There are versions for each release of MATLAB.

Version 2005 of PPLANE requires java 1.1.6 or above.

The botton below activates PPLANE within your browser. It computes the trajectories of a II order continuous time system (2 first order differential equations)

Before using PPLANE, you can look at the training exercise on the cycles in non linear systems.

AUTHOR'S NOTE
dfield and pplane are copyrighted in the name of John Polking. They are not in the public domain. However, they are being made available free for use in educational institutions. This offer does not extend to any application that is made for profit.

NileSim
This program simulates the hydology of the Nile river systems from sources to the Mediterranean and allow to evaluate the effects of alternative decisions on dams, canals, barrages to control the flow. 

Clicking here you can read a paper the describes the problem and the software. 

Anima-LP

A Java applet to solve and visualize the solution of a 2 variable linear program.