This set of applets are built on an extendable fractal engine. It is capable of zooming in on the fractal, changing the resolution, from within the applet, and switching between Mandelbrot and Julia Set equivalents.

It is so easily extendable, you can create another applet that extends the original Mandelbrot applet to use a different formula, without any loss in functionality, and by only writing about 10 lines of code. Some examples are available on this site, including the Mandel3, Mandel4 and Phoenix fratal types. These three include source code.

In the box at the bottom of the applet, there are a number of
controls. The first is a list box, which allows you to select the
resolution. The last three are buttons; the first just redrawing the
set, the second allowing you to select a region with your mouse, and
the last alows you to switch between Mandelbrot and Julia Set
equivalents. If you are switching to a Julia Set, it will prompt you
for a point, to use as *c*.

The applet can take a number of parameters. These are:

`top, bottom, left, right`- These parameters specify the window to use.
`type`- This specifies whether to do a Mandelbrot or Julia Set. Its value must be mandel or julia.
`creal, cimag`- Specifies the real and imaginary parts of
*c*. Only effective if`type = julia`. `maxiter`- Specifies the maximum number of iterations.
`resolution`- Specifies the initial resolution. Must be 1, 2, 5 or 10.
`nocontrols`- If set to true, the controls are not displayed at the bottom of the screen.