The mfpic4ode is a set of macros for drawing direction fields, phase
portraits and trajectories of differential equations and two
dimensional autonomous systems. The Euler, Runge-Kutta and 4th order
Runge-Kutta algorithms are available to solve the ODE's. The picture
is translated into mfpic macros and MetaPost is used to create the
final drawing. The package is intended for LaTeX, but it can be used
in plainTeX as well. 

Online demonstration of the mfpic4ode macros is available on
http://wood.mendelu.cz/math/mfpicpreviewer/ as Example 6.

You can get the documentation but compiling mfpic4ode.dtx file and the
files for installation by compiling mfpic4ode.ins by LaTeX.