Agco offers two manual tranny's with the shuttle feature. The 8 + 8 has 2 ranges, the 12 + 12 has 3. With either, you can shift between gears in the same direction and range just like an automotive manual. You cannot shift between ranges without stopping, or at least it isn't synchronized so you'd need to be quick and good to do it.
The 8 + 8 shuttle requires you to push the clutch in, the 12 + 12 does that for you hydraulically. The former is called the synchro shuttle and the latter is the power shuttle. I think the 4 speed box is the same for both, just with different transfer cases. You can go backwards just as fast as you can go forwards with either.
Deere's collar shift is a typical tractor gearbox. You pick your gear while motionless, let out the clutch and go. Shifting on the move is possible, but they didn't call them crashboxes back in the 30's without reason. The gears are not synchronized.
They also offer a synchronized box, a normal mechanically controlled hydro, and the electronically controlled hydro which opens up the door for all kinds of neat things if you trust the electronics and want to pay for it. Load match effectively slows the tractor and adjusts engine speed in response to the amount of work you ask the thing to do. The power reverser is an electronically controlled shuttle on the ehydro unit which allows you to choose between two different rates for slowing the tractor automatically as you run back and forth using the loader. Then all you need to do is move a little lever controlling the electronics.
