The Flash Dock from Pocket Demo is a DSLR hot shoe device that physically connects your iPhone (or other smartphone) to your DSLR camera, boosting the IQ of the latter by some margin. To what end? With the right apps, a smartphone can be paired with a DSLR for numerous purposes. Flash Dock plays no active part in the functioning of any of these apps - and you don't need a Flash Dock to make use of them - but by mounting your smartphone above the camera, the idea is that it provides ready access at all times.
Read the full article: Flash Dock attaches iPhone to DSLR, raises camera's IQ