Rationale: For a project I needed to mount an LCD in a small, thin part of an enclosure, with an Arduino + GSM shield somewhere else in the box. I ended up soldering flat cable to all the required pins, which sparked the idea for this product.
It's similar to the awesome Mama shield from Seeedstudio or Liquidware's Extender shield but with more flexibility in mounting. You could use one FPC shield on an Arduino (or other board with R3 layout), and use FFC's to connect up to 4 of the same shields with other shields on top. You could even daisy chain shields, but there are practical limits to signal and power integrity that are dependent on the application, the shields used etc. Because of the flexibility of the cable, you can even mount part of your electronics on a rotating part, through a hinge, on a sliding part etc.
Available separately is a 40 pins 0.5mm 150mm FFC. You could use your own cable, but there are some considerations (pitch, opposite contacts, not too long) to keep in mind. **Also keep in mind that you'll need at least two of these shields**, or roll your own PCB to connect to. The pinout is available on Hackaday.io.
A set of R3 stackable headers is included, but not soldered. So you're free to use other headers or solder a shield directly onto the FPC shield for a very thin connection. The shield is about 4mm high without headers. If you mount it on a headerless Arduino Leonardo, the package is less than 10mm high.