The quickest way to describe what Fritzing is about, is to quote the first paragraph on their site:
Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to work creatively with interactive electronics. We are creating a software and website in the spirit of Processing and Arduino, developing a tool that allows users to document their prototypes, share them with others, teach electronics in a classroom, and to create a pcb layout for professional manufacturing.
It has been around for a while, evolving and improving at a steady pace. Here’s a screen shot of the main window:
The neat bit is that support has now been added for the JeeNode, as well as support for the main two prototyping / extension mechanisms, the JeePlug and the Carrier Card. Just search for the “JeeLabs” keyword:
So now you can use Fritzing to design and document projects, and create printed circuit boards for them!