The 1990s was a time of great innovation for the auto industry, with many of today's most revered cars hailing from the era. JDM classics like the Mazda RX-7 and Nissan Skyline hit their peak during the decade, and high-end machinery like the McLaren F1 and Ferrari F50 pushed the boundaries of what people considered possible with a supercar. In a time when so many incredible cars made it to production, it's easy to forget about the concepts that could have been equally game-changing but never made it into the hands of customers.

RELATED: These Concept Cars Would Be Horrible To Daily Drive

This was for a variety of reasons: in some cases, manufacturers didn't believe that there was a good financial case to develop the car ready for production, or they believed that it simply wouldn't sell even if they did. Some of them considered production runs, but ultimately they never happened, and frankly, that's a huge shame. Whether they were cutting-edge supercars from an unlikely manufacturer or a six-wheeled version of a best-selling pickup, the range of ideas on show here is both weird and wonderful in equal measure. Let's take a closer look at ten of the best '90s concept cars that never managed to make it onto the production line.

10 Alfa Romeo Scighera

Alfa Romeo Scighera
Via Alfa Romeo

Alfa Romeo is still struggling to find enough new customers to turn a profit today, but back in the Nineties, their financials were even shakier. The Scighera was a radical attempt to change the fortunes of the company by creating a supercar, something that Alfa had never done before.

Alfa Romeo Scighera
Via Alfa Romeo

The Scighera concept was fully functional and featured a 3.0L V6 making around 400 hp, mated to a six-speed manual transmission. A mid-engine, AWD layout put the car firmly into supercar territory, and the Giugiaro-penned design was certainly a head-turner. The company planned to make a limited production run and even made a racing version of the car, but unfortunately, those plans were scrapped for unknown reasons.

9 Dodge T-Rex

Dodge T-Rex
Via Dodge

Today, the idea of a 6x6 pickup is nothing new, as everyone from Mercedes to Hennessey is now making them for wealthy clients. But, back in 1997 when the Dodge T-Rex debuted, the idea was still much more novel. The concept was powered by the trusty 8.0L Magnum V10 that also featured in the production 2500 and 3500 of the same era.

Dodge T-Rex
Via Dodge

While the Dodge 6x6 never made it to production, the company was owned by Mercedes at the time, and it's thought that the T-Rex was the original inspiration for the production Mercedes-AMG G63 6x6. However, it's still a shame that this delightfully retro truck couldn't have made its way to customers in its original form.

8 Nissan Trail Runner

Nissan Trail Runner
Via Nissan

The Nineties were a time of daring experimentation among Japanese manufacturers, with many weird and questionable concepts making their way to auto shows during the decade. The Nissan Trail Runner is one of those unusual prototypes, but it's actually a pretty cool one.

Nissan Trail Runner
Via Nissan

It took a different approach to Nissan's other concepts, channeling inspiration from American classics like the Plymouth Superbird but combining that with a higher ride height and off-road capability. There have been several other attempts since, but the "off-road sports car" segment has never really taken off, which is disappointing as concepts like the Trail Runner showed there was potential in the idea.

7 Renault Espace F1

Renault Espace F1 and F1 car racing
Via Renault

There are no two ways about it: the Renault Espace F1 was a crazy idea. Taking the company's best-selling minivan and turning it into an F1-inspired race car was a stroke of genius from the brand's marketing department, as the car drew huge amounts of attention from the press and the public at the time.

Renault Espace F1 and Renault Espace side by side
Via Renault

As cool as it was to see the Espace F1 being paraded at car shows and driven by racing drivers, it would have been even cooler if Renault had created an ultra-small production run of the car, perhaps just a handful of examples. They might not have been the easiest things to sell at the time, but they'd surely have novelty value in today's market. And anyway, the idea of millionaire collectors feverishly bidding over one of these things at a modern auction is enough to justify a production run by itself.

6 Bentley Hunaudières

Bentley Hunaudieres
Via Bentley

Throughout the Nineties, VW Group had been on a buying spree, snapping up both Bentley and Bugatti in quick succession. There was a lot of debate between executives about what to do with these newly-acquired brands, and one idea was to make Bentley into a supercar company.

RELATED: 8 Rarest Bentleys You Probably Didn't Know Existed

Bentley Hunaudieres
Via Bentley

As proof of that idea's viability, the Le Mans-inspired Hunaudières was created, with a 623 hp W16 engine and AWD. Eventually, it was decided that Bentley would stick to making luxury GTs and fellow newcomer Bugatti would produce supercars instead. The Hunaudières design was handed off to Bugatti's engineers and eventually helped influence the development of the Veyron.

5 Volkswagen W12

VW W12 Nardo
Via VW

While VW Group was busy making cutting-edge Bentley supercars, it was also debating whether to make a performance vehicle under its own name. The W12 concept was shown off in several forms between 1997 and 2001, featuring a mid-engine layout and a W12 engine each time.

VW W12 Nardo
Via VW

The design was penned by Italdesign and wooed enthusiasts and critics alike, but VW eventually decided not to press ahead with a production version. The W12 engine lived on though, enjoying stints in the production VW Phaeton, Audi A8, and Bentley Continental GT.

4 Ford Indigo

Ford Prototype
Via Ford

One of Ford's most visually striking concepts ever, the Indigo was a fully-functional prototype that debuted in 1996. It featured a mid-mounted 6.0L V12 and took heavy inspiration from the Ford Indycar program, hence its similar name.

Ford Indigo
Via Ford

It's not known whether Ford ever seriously considered putting the Indigo into production, although it seems unlikely given the Indigo's highly complex construction and use of emerging materials and technology. The company continues to own the functional prototype today and occasionally shows it off at events.

3 Audi Avus Quattro

Audi Avus
Via Audi

Originally shown off at the Tokyo Motor Show in 1991, the Audi Avus was intended to be a demonstration of the company's new aluminum space frame technology which eventually made its way into a production car, the range-topping A8, a few years later in 1994.

Audi Avus
Via Audi

The car's design was reportedly inspired by the vintage Auto Union racing cars of the 1930s, and it featured an early version of Audi's W12 engine that was again debuted in the A8 a few years later. Even if most of the technology from the Avus eventually found its way to production, it's a shame that Audi never made anything with the Avus' sleek exterior design.

2 BMW Nazca M12

BMW Nazca M12
Via BMW Media

Another futuristic V12-powered supercar, the BMW Nazca M12 was the closest the brand came to making a direct successor to the M1. It made around 300 hp and shared its engine and several other components with the production 850i.

RELATED: The Coolest BMW Concepts You Need To See

BMW Nazca M12
Via BMW Media

That would have meant that translating the M12 into a production vehicle would have been considerably easier than some of the other cars on this list, as half the components were already being produced. However, BMW never made the car available for public sale, although the Sultan of Brunei reportedly convinced the company to make a one-off version just for him.

1 Ford GT90

Ford GT90
Via NetCarShow

Possibly one of the most famous American concept cars of all time, the Ford GT90 is a masterclass in failing to capitalize on good publicity. Unveiled in 1995 at the Detroit Auto Show, the car captured the imaginations of fans worldwide with its new-age design and world-leading performance figures.

Ford GT90 rear
Via Ford

It shared a lot of components with the production Jaguar XJ220, as Ford owned Jaguar at the time. However, its engine was unique, a 12-cylinder design based on Ford's modular engine family. Ford originally planned to put the GT90 into production, but eventually, delays and setbacks meant the project was axed, and the company didn't make a new halo car until the release of the GT in 2005.