Although it's called a "cap," the tool mainly consists of two heat-treated steel hex wrenches that extend down from a rubber stem cap into the existing steerer tube. You just pull them out to use them. The wrenches have different bits at each end, allowing for choices between T25 torx, 4mm, 5mm or 6mm hexes – depending on which end of which wrench is used.
Additionally, it's possible to fit the two wrenches together end-to-end. This provides added leverage if a bit at the "long end" of one of them is being used. A cover screws onto the cap, to keep them secured when not in use.
The Dialed Cap reportedly works with any metal 1-1/8-inch steerer tube, although it is not recommended for carbon tubes. It's currently available for a pledge of US$35, with shipping expected for November if all goes according to plans. The estimated retail price is $50.
And should you prefer that your stem cap tell the time … well then, you might want to check out the StemCAPtain.