Generation 2 - The Cartomizer
This was the same technology that brands like Kanger used in their devices, and is basically the same principle behind almost all modern day vapes.
The first mainstream products that came out borne from these ideas was called eGo vaporizer. The Joyetech eGo-T was released which biased the ability not only to be modular in the sense that a user could swap tanks, mouthpieces and the battery unit, but it was also refillable and when the atomizer burnt out, they could just change the coil and it would be good as new.
This specific technology is still used today in most vapes, the main difference between them all is the makeup of the coil and the wicking material. Simply put, all modern day e-cigs have a battery for power, a metal coil (stainless steel, nichrome, kanthal etc), a wicking material which is usually cotton, and a tank or some sort of reservoir to contain the liquid.