Do hypercrackers work with freewheels? I thought only with freehubs?

I guess the first thing to determine is whether the wheel uses a freewheel or hub. Anything new is probably a freehub.

In the case of freewheels, the ratchet mechanism is in the cog seembly. It can break eliminating, forward drive. To make maters possibly worse, a fair number of the currently available assemblies are bottom of the barrel units, so one may end up having to splice a nasty part to the Phil uber hub one buys. To fix such failures one needs a means of getting into the back of the freewheel. The good news is that the fix is pretty easy and one reason why some like dealing with freewheels rather than hubs.