Cessna 0-2 and Dornier Do-335A

Both of these aircraft are unique in the aviation world for having both a rear and forward propeller. The Cessna 0-2 was developed for psychological warfare in the Vietnam wars and is powered by two engines. It also belongs to the twin boom family. Meanwhile the Nazi-German Luftwaffe Dornier DO-335A has both a similar engine layout, except the rear propeller is engine less. 

The Germans required a new fighter and despite plans laid down in 1942, it was not produced until late1944. At end end of World-War-II only about 30 aircraft had been built and 80 remained unfinished.

The Cessna O-2 Sky master has been built in the thousands and under licence in France as the FR-337. 

Performance wise, the Dornier was much faster. But by 1944 it was being superseded by the early jets. 

The O-2 could operated high-low and had a good range. 

Recently it has been discovered that this type of layout is much more economical on fuel consumption and a whole plethora of new types are being experimented with in the U.S. One of them being the Adam A500.

The Tractor.

The tractor was probably the first replacement for the horse, oxen drawn plow (plough) on the farm. Before that man had to open the earth literally by hand, but now there was a machine that could do it without him having to push. 

The threshing of cerials was already established through the use of the steam engine, but those heavy engines were not able to go over heavy soils.

Massey Ferguson reveloutionised farming with his tractor machines and nothing much has change since in the design shape. 

In Russia and the United states, the tractor machines are a different in shape and tracked versions have been produced.They of course are also much larger. 

Modern machines meanwhile have all the latest comforts from heating to swivel chairs and double driving cabs, lighting inside and out. Meaning that the machines can work day and night.

But it was the Chinese who came up with the mechanicle plough. In a basic 3-wheel design based on the movement of artillery pieces in Vietnam in the 1970's and since then this simple machine has been mass produced.