(Please bear with me as I edit this and add hardlinks.)
This is an

excellent program, especially for

high school students who are starting to learn complicated

geometric properties. You can

construct a

plethora^{1} of different

geometric figures:

And then, you can construct other figures onto one you've already put down. Ie, you

create a circle, place a point on top of it, then create a line through this point and the

center of a circle.

Using this program, I've successfully constructed

conic sections (

parabolas,

ellipses,

hyperbolas) and also illustrated problems for my

classes. (For those of us who have

visual minds, it is very

helpful to do this.)

Other things you can do:

You can also do

transformations on a figure:

You can do all sorts of

measurements. You can measure:

On top of all that you can enter an

equation where the

measurements are the

variables, and then use that to define some part of your figure.

A

locus is really neat. You start with a point that is defined to be on a

path (ie. on a circle or a line or

somesuch) and another point that is somehow affected by the position of the first point. You can then construct a locus, which is the set of all the positions that point 2 encounters as point 1 moves along its path. It then stays there while you

manipulate the figure. You can use this to construct say, a

parabola, and then move the

directrix and the

focus around to see how the parabola changes.

You can also

animate things, by telling the program to animate one point along its path and you can then see the rest of the figure

bend and twist or whatever as this happens.

You can also add in

labels,

colors (

pretty colors!) and

text.

The Geometer's sketchpad also comes with a very nice and

easy-to-use macro utility, it allows you to

recreate a construction you made multiple times and in

multiple projects.

Nice!
The Geometer's sketchpad was created by

Nickolas Jakiw and is ©

Key Curriculum Press. It works on

Win32, but older versions work on

Windows 3.1 as well.

^{1} I'm always looking for a place to use

that word.