Strangely, there is now something similar that is gaining in popularity and actually seems to work quite well. It's called the Power Plate.
This machine uses something called whole body vibration, a technology developed by Russia to use in its space program to combat the affects of zero gravity. Later, they used this technology to help train athletes; and you've seen variations of this in training methods like plyometrics.
Here is a picture of the Power Plate my5.
They claim that 15 minutes on this machine is the equivalent of about an hour at the gym. So how does it work? Well, as long as you understand that you have to exert some effort, the Power Plate works much better than I would've guessed.
At its simplest level, the machine vibrates 40 times per second. The movements happen in three different planes: front-to-back, side-to-side, and up-and-down. The movements are small enough, and happen so quickly, that they are rarely visible to the naked eye. Nonetheless, your body certainly feels them.
The Power Plate is a little bit larger than your typical doctor's scale. You stand on its platform while performing various movements or stretches. For example, imagine doing a deep knee bend and holding that position when your thighs are parallel to the ground (basically a half squat). As you hold this position, normally, your thigh muscles would get a decent isometric exercise – and you can probably imagine them burning a little. Now imagine what would happen if, as you are performing that exercise, the platform vibrated 40 times per second. Think how many more muscles you would engage. Think how much better this would be as a core stability exercise.
The Power Plate is designed to support a wide range of exercises for all of your main muscle groups – and comes with various accessories, like straps and mats. I found that many of the exercises I enjoy most are movements that my wife says are similar to yoga positions. I try not to let that discourage me from doing them.
The machine gets used every day. My wife and son like it too. It is exercise, and it does take work. With that said, it has had a noticeable effect on my strength, flexibility and my ability to do traditional workouts at the gym.
You can find out more about this at the manufacturer's website.
Here are some links about the machine and exercises.