I had a project last year that needed to run 4 small stepper motors (Pololu #1204). At that time, I used the Arduino Duemilanove (bottom) and 4 Pololu stepper motor drivers (on top) as shown below (sorry for poor picture quality).
It was bulky due to stacking the two with female headers and I hate the location of the header pins (#8 to AREF) of the Arduino Duemilanove which made me make curved pins using 22 gauge wires as you can see in the above picture.
Anyway, after building this combination, even though it worked fine, I found there were lots of minimal Arduino compatible boards as mentioned in earlier post.
So I thought I could design a new board with the minimal Arduino components, 4 Pololu stepper motor drivers and the FTDI USB breakout board from Sparkfun on one compact board as shown below. Actually there are other components on the board (palm size) for my whole project but those are not relevant to this post so I cropped the picture.
It works exactly the same as previous bulky stacked combination but occupies less space, thin and neat.
So I thought if I had a minimal Arduino board like the core part of the board shown above, which is nothing but yet another minimal Arduino, I could use it for many other projects and started designing the JeonLab mini.
I hope there is someone else to find it useful.