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Adafruit Particle Shield Shield for Photon [ADA2725]
The Particle Shield Shield converts the footprint and pins of your Photon into that of an Arduino, allowing for use of existing Arduino shields and accessories.
This shield converts the pin mapping of the Photon to the Arduino pin layout and provides a voltage translation of 3.3V to/from 5V. Note that Arduino libraries are not necessarily going to work without some porting, but for many basic shields that do not depend on the specific Arduino chipset, this will get you that much closer to compatibility!
Mechanically compatible with both the Particle/Spark Core and the Particle Photon.