I have nothing to do with design, because I don't know how to mix two colors. Some time ago, I've read about some tools which are used in the creation of interfaces for application and web pages.
In that article were mentioned some tools, and one of them was a free firefox add-on. I'm not looking specifically for that add-on, but the idea is that those types of applications aren't very advanced in order to be used by professionals in the design field.
Do you have any idea about what I'm talking about? Can you name some of those applications?