I use Unigraphics (well now called NX3) everyday (its 3D) !!, its a very powerful tool when you get into it, been using all the Unigraphics since version 12, about 7 years now.

Its good if you get a full model of say engine block with pistons etc, and assign relevant mating conditions on the parts. You can then spin the crank and the whole assembly moves as it would in real life !!