I have a bit of a love affair with the AMT (that's an Adaptive Motion Trainer for the uninitiated), so I'm a bit sad it's landing in the middle of the pack at number six. You see, the AMT is like a better version of an elliptical trainer, offering a nice low-impact alternative to jogging on a treadmill. Unfortunately, elliptical trainers as a whole aren't very functional.
What sets the AMT apart from traditional ellipticals is that it actually offers two degrees of freedom, allowing the user to adjust stride length and height, which more closely follows a standard step.
Is it perfect? No. A typical stride length on an AMT is only about 70% of that during jogging, while stride height ballooned to 150% of a typical jogging step. These numbers aren't ideal, but they beat the crap out of the numbers seen on a traditional elliptical, which only offered a stride length of about 60% of a typical jogging stride, with no ability to change stride length based on speed. Functionally, ellipticals suck.