Download this app if: you want to control your Canon EOS DSLR via USB.
DSLR Controller was the first and remains the best app to fully control your Canon EOS DSLR from your Android device with a USB cable. No computer or laptop required, no root required, only a compatible mobile device, a compatible camera, and the right USB cable. Compatible camera's and WFT boxes...
Snap — This seems like a great idea, providing you have the compatible camera. But, it's exciting that there may be apps like this for all different makes and models in the future.