Fractal4D is a great Designing Tool by Matt Kenefick, which allows you to draw beautiful line-shapes just like the blend option of Adobe Illustrator.

Fractal 4D allows you to draw beaiful technical looking figures. The lines follow your cursor and, dependant on your settings, change the color once in a while. You can almost edit everything.

This is great for creating lighting effects, your own Photoshop brushes, patterns or just graphic elements.

check it out ;)