If you'd like to see a couple of videos showing Opeke in action, look at noughmad.org
Opeke is a KDE4 application for building structures with virtual bricks. It uses OpenGL to render you objects in three dimensions, so you can see what you've built.
Please take a look at the Download section.
Building the bricks is pretty straightforward. For more complicated things, RTFM.
If you experience any problems, if you would like to request new features, or just want to share your creations, you're welcome to visit the Opeke forum.