DSLRs are the fanciest type of digital camera you can get, often costing many thousands of dollars. Pinhole cameras are the most basic and cheap form of photography out there, requiring just a pinhole and some film. And now a body cap for DSLRs combines the two.
This special body cap replaces the lens on a DSLR with a cover that has a tiny hole laser-cut in it. It's then covered with a thin, transparent film so no dust can get in. Think of it as the most high-tech way possible to make a very low-tech photo. It'll create completely unique photos, ones no fancy "real" lens could create, and the fact that it's attached to a digital camera lets you see the results in real time for easy experimenting and adjustments.
The only downside is that this thing is $50, which seems pretty high for a glorified lens cap with a hole in it. But still, it's a pretty neat trick.