We've had plenty of talk about the popular production cars in all segments, but what about the ones that you can't get your hands on? What about the most exclusive, unique, and forgotten cars devised by clever manufacturers in the last century? Scarcity commands value - as with art, so with cars. And owning something that no one else can own has a special allure to it, which is why the rarest of cars tend to fetch the highest prices at auctions.

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So, today, we run you through the most scarce and unique car models ever created, ones that you probably never heard of because they are no longer in production. Some were created with big future plans yet now lay forgotten by the mainstream automotive community, while others are merely an extravagant display of a company's ingenuity and competence. Whatever the case may be, the cars on this list are all unique and each tell their small piece of the lesser-known history of automotive. Enjoy!

10 Porsche 916

We bet you've never seen one of these before. Introduced in 1972, the 916 is actually a big brother to the now iconic 911, and flopped due to the steep price it commanded. For this reason, it's now fabled as one of the rarest Porsche models ever created by boasting a production run of only 11 units.

By no means is this the car's fault. Considering it was created in the '70s, the 916 has an interesting design and a more-than-decent 2.4L engine, producing 190 horsepower and guaranteeing a top speed of 145 mph.

9 Bugatti Royale Kellner Coupe

Few cars can come close to the level of dignity and luxury the Royale Kellner Coupe boasts. Created by Ettore Bugatti in 1931, it was aimed strictly at royalty and envisioned as the most luxurious automobile in the world. Even today, its giant stature dwarfs luxury leaders the likes of Rolls Royce Phantom by a large margin. It stands at 21 feet long, while just the massive hood ornament easily reaches eye level.

To stand in the presence of this car is humbling, and the thunder of the 12.7L double straight-eight engine hiding under the colossal hood will send shivers down anyone's spine. We're talking about perhaps the biggest engine ever put inside a production car, one that'd able to roar with 300 horsepower - an inconceivable number in 1931, when the car was new. All this extravagance and luxury met a quick end when the car's production had ceased due to the economic depression, with only six of these cars ever seeing daylight. They are still out there somewhere today, and we know that one of them sold for a staggering price of $9.7 million in 1987. Adjusted for inflation, the price would come out to about $20 million today, putting it among the most expensive cars ever sold.

8 Aston Martin DBR1

Even 60 years since it had won the 24 Hours of Le Mans, the DBR1 is still considered the very pinnacle of Aston Martin performance cars. The car is a classic masterpiece, put together by a small and focused team of engineers to outperform all other cars in its era.

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Today, it stands as a monument to Aston Martin's achievements, with only 5 models in existence. One of them was sold at a 2017 Monterey Auction by RM Sotheby's for a staggering $22,5 million, making it the most expensive British car to ever be sold at an auction.

7 Oldsmobile F-88

Of all classic American muscle cars, the 1954 F-88 might be the rarest. This perfect embodiment of the 1950s automotive aesthetics is today listed at Barret Jackson's Auctions at a steep price of $3,300,000.00. And while four have been created, the one depicted above is the only model that survived. The chassis it rests on is actually borrowed from a Corvette, but that's where the similarities end.

The F-88 was namely envisioned as a beautiful luxury convertible and the concept's bodywork was made out of fiberglass. The engine it uses is a substantial 5.4L V8 producing 250 horsepower, which made it quite a beast 60 years ago. The car also hides many surprises, such as the spare tire behind the rear bumper and the radio between the driver and passenger seats.

6 Ferrari F50 GT

Upgraded from the Ferrari F50, the F50 GT was envisioned as a car that would stand up to McLaren and Porsche on the race track, and so became the most extreme Ferrari to come out of the '90s. However, when the Porche 911 GT1 - a car designed specifically for the race track- came out, Ferrari found themselves outmatched by the rival and ceased the production of the F50 GT.

Today, it stands as one of the rarest Ferrari models ever, with only 3 units ever seeing daylight. Under the bonnet is a beastly 4.7L V12 engine using 750 horsepower to launch this 23-year-old car to 60 in under 2.9 seconds and to a top speed of 236 mph. The price for one of these is now counted in millions.

5 Koenigsegg CCXR Trevita

The name Trevita translates to "Three Whites." This is because this elite hypercar was envisioned to be limited to three models, each utilizing a unique technology that changes the color of the carbon fibers making up the body of the car from the traditional black to a silvery-white. However, the complexity of this unique manufacturing process resulted in only two units ever being produced, making the Trevita extremely rare and desirable.

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But that's not all, the car is special on the inside as well due to the monstrous 4.8L V8 engine that develops 1018 break-horsepower, allowing the Trevita to reach 62 mph in just 2.9 seconds and exceed the top speed of it rival Bugatti Veyron. To own one of these, you would have to set aside no less than $4,8 million.

4 Icona Vulcano Titanium

Feast your eyes on the first ever car entirely constructed out of titanium. When building the car, it took an alleged thousand hours of hammering to get the notoriously tough titanium into the desired shape.

That's not the only unique and defining feature of the Volcano Titanium, though: it's a flat out $3.8 million dollar Hypercar, and there's only one in existence like it. The Volcano sports a 6.2L V8 that erupts with 670 horsepower and shoots the car to 60 mph in just 2.8 seconds, eventually claiming a 220-mph top speed.

3 Maybach Exelero

Although it represents the epitome of Maybach luxury and extravagance, the Exelero was actually created for the sole purpose of testing out performance tires. And test them it did: weighing in it at a massive 5863 lbs (2900 kg) and spanning 232 inches in length.

Under the hood of the Exelero hides an equally massive 700-horsepower 5.9L V12 that transforms this land yacht into an all-out supercar able to reach a baffling top speed of 218 mph. There is only one Exelero in existence, and it used to be owned by the rapper Birdman, who purchased it in 2011 for a price of $8 million.

2 Aston Martin Bulldog

The Bulldog is one of those unusual looking concept cars from the '70s that are both silly and intriguing at the same time... and angular, of course. Influenced by the '70s automotive trends lead by the likes of the Lamborghini Countach and Lancia Stratos, Aston Martin set out to create something entirely new and out-of-character in 1979. The result was a mind-numbing supercar concept that looked like a prop left over from a sci-fi movie set.

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They named the angular spaceship the Project K.901 after Doctor Who's dog. Later, the nickname Bulldog would prevail, as the car was more beastly than any of its competitors. Inside it, they placed a 5.3L twin-turbo V8 exploding with at least 600 horsepower, which meant a 192-mph top speed for the Bulldog. On paper, Aston Martin figured it could even reach 237 mph, which would put it ahead of all the modern Martins. However, the changes in company leadership resulted in only one ever leaving the production line. It's still out there somewhere today, bought in 2011 for $1,3 million and now sporting a fresh green color.

1 Ferrari 250 GT Spyder Convertible

There are plenty of 250 GT Coupes, but only one convertible. This is what makes it so special. The car carries a beautiful mid-century beautiful Ferrari look that's unique and instantly recognizable. This convertible is owned by a car collector named Bob Lee, who purchased it for $9,500 from the great Enzo Ferrari himself at the 1956 New York Auto Show. The interesting thing about that is that the cost to produce the car was about $20,000. Lee greatly underpaid for the car, especially considering it's the rarest Ferrari in the world, worth an estimated $10 million today.

Perhaps Enzo knew exactly what he was doing when he gave the car to Lee, possibly recognizing a suitable owner for his prized Ferrari in him. And indeed, the car remained in Lee's possession for over 60 years, as beautiful as the very day it was bought.

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