"Project Buggy" was the first project I released in to the wild. I used Eagle CAD to design a single-sided board. I used the toner-transfer method to etch the board and made about 20 of them for a family reunion.
In wanting to share my designs with others, I documented it at Instructables.com. It was "Featured", putting it on Instructables front page for a bit, and that resulted in thousands of views. I would learn later that being featured was a high-bar to attain. To my knowledge, only one other person built a buggy, and he used circuit boards that I sent him.
While the cost of the project was good, about $8 in parts, but two other hurdles kept it from being a great project. First, setting up a software tool-chain to program the chips was difficult. Second, etching your own circuit board is not trivial and requires some pretty nasty chemicals.
OSHpark or BatchPCB is getting easier and programming attiny chips can be done with the Arduino environment now. I hope to revisit this project in the future.