2006 Volkswagen GX3 concept was a Tron trike for the streets

Of all the concept vehicles on this list, the 2006 Volkswagen GX3 probably came the closest to production.

This crazy three-wheeler debuted at the 2006 Los Angeles Auto Show to rave reviews.

The company developed prototypes and a business case, and it was sailing toward dealers when VW's lawyers stepped in and put a stop to the fun.

Apparently, the idea of selling something like this with no doors, no airbags and no stability control worried Volkswagen's legal team to no end.

Designed in VW's California design studio, the GX3 weighed under 1,300 pounds and was pegged to cost under $17,000 to start -- around $4,000 less than a base Mazda MX-5 Miata at the time.

The rear-wheel-drive trike was powered by a 1.6-liter four-cylinder engine paired to a six-speed manual gearbox.

VW claimed 0 to 62 mph could happen in 5.7 seconds. Plus, the GX3 was supposed to get 46 mpg on the European fuel-economy test cycle.

Yes, that golf-ball shift knob is an homage to VW's famous GTI.

It looks pretty snug in there, but in a good way.

While the GX3 never did make it to market, other companies, including Polaris, have found a not-insignificant amount of success with the three-wheeled autocycle formula.