The ultimate example is of course the FMR Tg500. It’s usually called a Messerscmitt Tiger but it wasn’t actually either of these. Messerschmitt acquired the design of the three wheeled Kabinenroller and when that showed signs of no longer being a thing - and they were allowed to make aircraft again - they transferred the rights to FMR who then got the idea of something with a bit more go and one third more wheels. Oh, and a reverse gear. The three wheeler relied on a reversing engine, just like large ships today.
Enter the Tg500 which as you might expect a 500cc engine in place of the 175 and 200 units of the three wheeler. It went really quite well, but not in sales terms with only 320 made. Like quite a few other sales failures the surviving ones - which is most of them - are worth a fortune.
Like this one
By way of contrast, here’s a less pampered one being actually used