Greatest invention a man ever invented....  

Soap. Hygiene is extremely important and helps us stay clean and helps prevent diseases that we would carry if we weren't able to clean ourselves and bathe ourselves. It's such a simple thing, but it is massively important to our society for so many various reasons. It's one of the many steps that brought us towards true civilized living and self maintenance via hygiene.

For me its electricity, everyone is dependent on the power supply machines, work or even at home just a simple light is powered by electricity.

well every invention is good depend on its use but for me the greatest invention human made is the florescence light, it help us see in the dark, I'm afraid of the dark so that the reason why florescence light is the best for me.

Man's greatest invention according to me is the wheel.
Without the wheel , you would not find yourself in a vehicle.
Imagine everyone riding on horses, elephants and other animals - we would be causing burden not only on ourselves but also on the animals.
The wheel marks an important discovery in mankind.

The wheel gave birth to a hand cart which gave birth to a bicycle, car and other vehicles. The wheel is modified as tyre and used in even planes.

For me it's the transmission and reception of signals. I don't know who found out about it but if it's not present then cellphones, internet, radio stations, wouldn't be present today.