What is Konstruktor?
Konstruktor provides a 3D environment on your screen in which you build Lego models out of predefined bricks and other subunits. The program comes with well over a thousand pieces already available, and as you make new items you can save them as submodels and use them repeatedly in your finished scenes. The rendered scenes scale up or down depending on how many pieces there are, and can be saved in JPG or PNG format.
The official website is no longer available. Last version, 0.9.0-beta1, released in January 2011, and the sourcecode are still available on Github.