Every automaker has experimented with concepts over the past decades, but most aren't too keen to show off what could have been. 

Porsche? Not so much. The brand has curated its top five secret prototypes for the latest in the ongoing "Top Five" YouTube series. As the title suggests, the latest episode looks at five obscure prototype cars many likely have never seen before.

Number five is the Porsche 984 prototype. The 984 looks nearly production ready and was meant to hone in on the ability to achieve a roadster with compact and lightweight proportions. The 984 weighs just 1,940 pounds and makes 133 horsepower. Engineers worked to achieve Porsche's fundamental driving characteristics with low resistance and lightweighting, rather than through power alone. The 984 never made it to production, but it certainly influenced another production car: the Boxster.

Moving onto number four is one we're mighty glad never made it to production. The Cayenne Cabrio was quite possibly ahead of its time, because it was built well before Nissan and Land Rover created their own "crossover convertibles," but boy, it's not pretty. Porsche worked on the prototype in 2002 and it was a work-in-progress design study. The car never made it much further, as engineers and designers decided to make two prototypes into one. The rear of the Cayenne Cabrio prototype sports two different designs. The driver's side design is arguably better looking, but it's best Porsche keeps this one locked in the basement, in our opinion.

Number three is something really special: a 911 Carrera Speedster Clubsport. Specifically, engineers worked on the car in 1987 and set out to create an open-air single-seat car that recalled Porsche speedsters of the past. Just one small windshield deflector sits in front of the driver. The concept ended up being a precursor to the sought-after 911 Carrera Speedster.

Moving right along to number two, we arrive at the Porsche Panamericana. The prototype was built as a gift to the brand itself to mark the 80th birthday of Ferdinand Porsche in 1989. The prototype came to life in just a few months, and like the Cayenne Cabrio, we're glad some of the more dramatic design cues didn't find their way to any production cars. However, the neat removable-zipper roof strongly influenced targa-top models to come.

And number one? That awaits viewers in the video above, but it comes from the relative modern day.