Geez... A real response here:
FREECOASTER: A freecoaster is a complete rear hub design that includes an internal clutch that disengages from the hub when the rider stops pedalling forward. This clutch requires about 1/16th of a crank to engage the hub, so the slack before you go anywhere is pretty significant on it. But, when the bike is rolling backwards the pedals do not shift unless you pedal forwards. If you try this on any bike with a freewheel (or cassette) you will find that the pedals spin backwards when you are rolling backwards. Freecoasters were originally modified coaster brake hubs (like when you were a kid and backpedalled and the brakes came on: that's a coaster brake hub). Now, Nankai really reigns supreme in the freecoaster department with very high quality freecoasters and one-piece drivers (don't strip out) down to 11 teeth, perfect to match with a small front sprocket for more room to maneuver.
CASSETTE: A cassette is also a complete hub assembly, but this one ends up acting exactly like a freewheel. That is, when you pedal forward, you go forward, when you stop pedalling you hear a clicking sound, when you roll backwards the pedals shift backward. (note: freecoasters are silent when you stop pedalling) People get cassette hubs because they are supposed to be stronger than your average freewheel (not all are though!) and more importantly, you can run rear sprockets down the 9 teeth on some of them. This allows for (once again) the smaller front sprocket and more room under the bike to maneuver around stuff. Some cassette hubs use special technology that completely eliminates any slack from pedalling. So, the moment you pedal forward, the cranks engage and you are accellerating. It is very noticable, but not necessarily as reliable of a technology.