Dynamic Geometry
Dynamic geometry programs are powerful educational tools for teaching and learning of geometry, and sometimes even other areas like algebra and calculus. Basically, it allows students or teachers to construct and measure geometrical figures that can be easily modified with the mouse based on the geometric relations specified by the user, thus supporting demonstration and exploration of geometric concepts. The first 3 items below are popular and well developed commercial programs of this kind. The others are freeware performing similar basic functions.
The Geometer's Sketchpad  
Cabri Geometry II plus  
This folder contains some examples of 3D figures created with Wingeom
Cabri 3D is a new interactive solid geometry software, evaluation version is available; construct and manipulate 3D figures
GeoGebra is a freeware incorporating most common tools in geometry, algebra and calculus. It has a Chinese interface and could export files as Java applets.
Links to resources in Dynamic Geometry