It's called the Nautilus Step walker, the first time I saw it I was skeptical, meh another stupid cardio thingy for the Gym Tourists, but than I saw a friend of mine on it and he said it's the best Cardio machine he ever had, so I tried it out and I tell you guys that thing rocks:
It works like a Treadmill but the "band" you walk on split in the middle and the two parts go up and down, so it feel like you are walking uphill and at the same time get up steps.

a) There is practically no pain in the joints
b) You are somehow walking upwards but at the same time as on the step machine, it's much much harder than you first believe.
c) Speed doesn't go higher than 6.4 what is perfect for fatloss and it keeps those annoying *I run like an elephant and don't care what sound the treadmill makes* guys (or fat girls)
I have found out that you can intesivy the workout even more when you not hold on but try to walk free hand and lean slightly forward.
I'm more the kinda guy that believe what was good for the guys and gals years ago will be good today, than believe in all new things, but damn that thing is good.
I'm sure of you have that thing in your gym, it's extremely pricy but damn it's good.