Magic Box

Magic Box is a pretty amazing tool you can use to create parametric designs in your browser than can be edited on the fly. If you create a design and decide later that the width needs to be longer than you originally created it, no problem, just adjust the slider and it automatically configures everything else around that adjustment. The designs are created using code, and while it may take a bit of practice and preparation, through the tutorials you can be on your way to creating your own designs using this. There are also some sample files you can load up, view the code used to create them, and adjust those parts as well.

http://magic-box.org/