The gym I train at recently purchased a bunch of new equipment, all Startrac brand. Most of the stuff is functional cable equipment, but we also go this new smith machine called a Max Rack. I have heard of 3-dimensional smith machines but never had used them.
This one moves up and down and back and forth, the only motion it cant perform is any tilting. But let me tell you, as far as smith machines go, this thing is the shit.
You can power clean, deadlift, front squat or back squat perfectly with this thing. Its kind of funny because if you cant do a good free bar squat or deadlift, you wont be able to do one on this.
One of the morons in our gym went to try to squat and he almost fell over backwards because he was used to leaning back against the smith machine! Haha! The dumb fuck!
Not half as good as a free bar, but ten times better than a traditional smith.
Check out the cheesy commercial, but note the snatch people.