This might not seem like a revolutionary thing, but here's why I'm hooked: I've found this tool to be an efficient way to code and prototype ATtiny85 microprocessors.
|My digital breadboard, testing out code that I wrote for an ATtiny85|
Small microprocessors such as the ATtiny85 can be incredibly tedious to prototype, often requiring multiple boards and lots of wires. If you've ever tried connecting alligator clips to one, then you know that it's super tricky to keep the clips from touching one another while you're testing out your code.
That's where 123D Circuits can come in handy! Rather than having to set up a breadboard (or get out the alligator clips) every time you want to test your code, you could use a digital breadboard to do it instead. Then, once you've verified that your code is doing what it's supposed to do, you can save it (along with your breadboard), making it easy to access and build upon later.
Paired with CodeBender and a Chromebook, I've found that not only can I test my code and wiring virtually, but I can also upload it right to my ATtiny85, using Arduino as an ISP.
Although 123D Circuits has a lot of useful digital components, such as LEDs, resistors, and switches, I have not been able to figure out how to digitally test out a light sensor on an ATtiny85. Also, there doesn't appear to be a sound sensor.