Here is a very fun roadster concept from BMW Technik in 1995: the Just 4/2. Also known as the Z21 internally, the rear-engine design was intended as a lightweight sports roadster in the mold of the Lotus/Caterham Seven -- but designed to be safe and road-legal worldwide. The UK's very forgiving road safety rules are all that allow their thriving mini track car industry -- so BMW hoped to take the sheer joy of an open-cockpit, open-wheeled plaything to a global audience.
Interesting details abound: the removable door panels keep their upper frame element in place for side crash protection -- even while you could reach out and grab some concrete around corners. We also love the slight windshield airfoil: a slight flip in the back edge of the mini windshield to just the air up and over passenger heads. The Just 4/2 could then be civil and fairly refined for passenger and driver up to around 65-mph -- all without the required helmets of many others from the genre. An extra smart touch? The lower wedge of windshield is glass -- letting you hide low in the seats, but still have a view forward.
And the firm was and is well-prepared to lead this charge. With a huge portfolio of motorcycle engines and expertise, it was just the expected price that put the Z21 concept on ice. BMW was deep in the launch of the Z3 at the time, so this makes sense.
A final curio? The year before, a Z13 prototype wearing a breadvan-style coupe design over this rear-engine layout...