Kids can be very interested in 3 dimensional shapes, from making simple pyramids to more complex shapes. Poly-pro is a simple little application that can really help to show how polygons can be made.
The interface is pretty basic, with one window for the polygon you are viewing, and another with the controls. Here you can choose the type of polygon you wish to view - there a number of categories to choose from and a large variety of polygons in each, ranging from the most basic to mind bogglingly complex.
You can change the color of your polygon, and with the mouse spin it around, and use a slider to 'unfold' the shape into its 2D net. Watching some of the more complex shapes assemble and disassemble themselves is quite impressive, and will certainly captivate students.
As well as viewing the shapes on screen, you can print them out, either in 3D form, or in their nets, which could be used to make real paper 3D models of polygons - great for school, and possible very time consuming for anyone who wants kids to keep quiet and concentrated for a while!
Poly-pro is not a complex program, but it displays polygons very well and will be interesting to anyone who wants to learn about shape.