Circuit Scribe is a rollerball pen that uses a silver conductive ink to let you create fully functioning circuits as fast as you can draw, making it cheaper, faster and easier to test out electronics and prototype concepts.
Developed by Electroninks Incorporated, a company originally part of a University of Illinois research lap, Circuit Scribe tries to make the process as easy as possible. No wires, no boards, no soldering; all you need is a sketch and you can begin tinkering with nothing more than a coin battery and an LED.
I’m a bit bah humbug about this and other instant prototyping systems like breadboards. You can easily test a circuit out with software simulation these days which, as a bonus, gives you access to a laboratory full of virtual test gear.
If a criticism is that simulation is a bit too perfect and doesn’t reflect real world limitations, then these instant hardware prototyping systems go the other way, with unreliable connections, high impedance grounds, excessively long wires and so on. A circuit built like this will fall apart if you breathe on it, and would almost certainly work much better on a printed circuit board or even on stripboard – which can be made to work quite well when covered with a copper tape ground plane.