An eVTOL aircraft can take off and land vertically. And it is, of course, powered by electricity rather than traditional fuel.

There are hundreds of eVTOL designs in the works, with varying technologies. Here’s a look at four of the most common.   

The “multicopter” operates like a standard drone. It has multiple propellers that help it fly. They are very efficient during take-off, landing, and while hovering, but because they don’t have wings, they’re incredibly inefficient at going long distances. They could be useful in urban areas.

The “lift & cruise” concept merges the multicopter with common aircraft technology, like wings, making longer distances possible. But to get the two technologies to work together, the propeller needs fewer and shorter blades — making it very noisy.  

Then there’s “tiltrotor” — a design which has one or more rotors mounted on a wing that can tilt up and down.

Finally, there are “ducted vectored thrust” models, which don’t have a propeller in sight. They use multiple, individually controlled electrical ducted fans to push the vehicle upward. This model is quieter and can fly longer distances efficiently, but are quite power-hungry.

So, aren’t these just glorified helicopters? Not quite. From the technologies they use to take off and land to the fact they’re electric, eVTOLs are trying to distinguish themselves from helicopters. Not to mention that helicopters are quite expensive too. Many eVTOL companies are talking about a world in which these vehicles become part of everyday travel in or between cities — at an affordable price.

Aviation regulators around the world are in charge of making the rules around eVTOLs. In Europe, that’s the the European Union Aviation Safety Agency. In the United States, it’s the Federal Aviation Administration. And in China, that’s the Civil Aviation Administration of China.

All of those regulators have put in place various rules and certifications that eVTOL producers and operators need to adhere to and meet before being able to take these aircraft commercial.

The certifications revolve around areas such as aircraft safety and pilot licenses.

While eVTOLs are currently being tested at dedicated sites, many aircraft makers are talking about a future where they will be in commercial use.

Some are discussing the possibility of eVTOLs operating within a city as a mode of urban transportation. Others are looking at ways these electric aircraft could be used for travel between cities, perhaps accompanying or replacing other modes of travel like cars and trains.

But infrastructure will need to built to support this. One key piece of infrastructure will be so-called “vertiports,” a type of helipad combined with mini airport where these aircraft will take off and land.

While some wealthy individuals may own their electric aircraft, they will more likely be operated in fleets by an operator, as is the case with airlines.

There are several challenges when it comes to adopting eVTOLs. Complying with regulations and ensuring they are safe is one of the biggest ones.

Perhaps the biggest challenge, however, is public acceptance and adoption.

Adoption could be held back if people perceive them as unsafe and if they’re expensive to use.

Alef Aeronautics has a different take on the eVTOL — a vehicle that can drive on the road and fly in the air.

The car’s chassis is hollow and hides a number of propellers. A video demonstrating how the car might work shows the vehicle taking off vertically and being able to fly on its side.

Alef Aeronautics has big ambitions to start production in 2025.

“If everything goes right, if we have enough funds, if the legislation does not get worse … we plan to start production of the first one by the end of 2025,” Jim Dukhovny, Alef Aeronautics’ co-founder and CEO, told “CNBC Tech: The Edge” in an interview.

The company’s most notable backer is venture capitalist Tim Draper, who was an early investor in Tesla, SpaceX and Theranos.

Customers can now pay a $150 deposit to pre-order the car — known as the Model A — which has a price tag of $300,000.