Shown here is only one example of Adult Trikes available from this source. See them all through the following link:
Browse all Adult Trikes here.

This particular example of available Adult Trikes is the Bike Rassine Hill Kicker Pro Street Trikes (20-Inch). I only decided to depict this one here because in my opinion it looked the coolest, however, many others are available. See more images and product details through the following link:
Read More About it or Buy it Here.

Pros: 

This example of the adult trikes is adjustable and uses a standard mountain bike stem for simple upgrades. Thick rear wheels that roll and glide with ease. Ships internationally in many cases.

Cons: 

The customer reviews on this version of the adult trikes is very mixed. You can read all reviews good and bad and judge for yourself. There are many other adult trikes from the same source that have better reviews.

This trike can be used by some kids but mostly adults, depending on your size. This is the Westport adult folding tricycle. It is an old school classic three wheel styled bike. What makes this one cool though, is that it is fold-able. You can see in the image where the frame can pivot and cause the bike to essentially fold in half for easy storage. In the back, you can see a mounted basket for extra cargo space for longer trips or to be used as a grocery getting vehicle. The upright handle bars are adjustable, and the seat is extra wide for extra comfort on your backside. This trike has 20 inch wheels and a suspension fork to absorb the shock of potholes or any other bumps in the road you might encounter.

These trikes shown here are called the Mobo Triton Ultimate Three Wheeled Cruisers. These are much more expensive, but you get what you pay for, and these are really cool. They are also good for kids and adults alike, as you can see from the family demonstration photo. They come in four different colors including silver, pink, blue, and red. Click the image for more details.