I just thought I'd share some weird ones I've learned about, in hopes of sparking a discussion. I hope someone can top these.
So let's talk about some weird motors:
The Commer "Knocker," a British post-war diesel engine used in trucks (lorries?), had three cylinders and six pistons. Two pistons per cylinder! https://en.wikipedia.org/wiki/Commer_TS3
That leads nicely into the Napier Deltic, which is a larger diesel engine (used in trains and ships) that had a weird triangular setup. Banks of six cylinders, arranged in a triangle (I guess you could call each side of the triangle a "cylinder"); three crankshafts, two pistons per crankshafts, and two pistons working in opposition (like the Commer Knocker) within each cylinder. Here's a short video of it (30 sec) from youtube: https://www.youtube.com/watch?v=Yftg5Ip0YlA
One of the really fun ones is the Chrysler Multibank, a World War II tank engine. It was a 30 cylinder engine built from five Chrysler inline sixes. Wikipedia explains it better than I can, with a picture: https://en.wikipedia.org/wiki/Chrysler_A57_multibank. Speaking of tank engines, maybe less weird and more wonderful is the modern M1A1 Abrams' turbine, which is said to make 1500 hp and can run on virtually any liquid that burns. My mind was blown when I first learned that our army tanks are jet powered! Strictly speaking I suppose it's not a jet, but still. Turbine cars are fascinating (some of the US automakers built prototypes in the 1950s-60s but it apparently never progressed very far) and it seems one of the only perfected, working, real-life models is in our very own tanks.
I'm sure some of the Soviet tanks have interesting engine setups--some kind of mammoth air-cooled diesel four-cylinder, I suppose--but I don't know much about those.
Lots of airplanes have radial engines, of course.
Then there's the Cizeta Moroder V16 engine. I'm not sure I fully understand what's so strange or interesting about this, but it pops up on all kinds of "weird engines" lists. Maybe it's just unusual. Apparently with the engine mounted transversely and the output shaft in the middle of the engine, this was essentially two V8 engines stuck together.
In the 1920s-30s, Bugatti made some "U" engines that were essentially two inline engines, upright and side by side, connected by gearing at the bottom to share a single drive shaft.
People have done all kinds of wonderful things with Mazda rotary engines. I was looking earlier for a YouTube video I once saw of a Miata with multiple rotary engines grafted together, but I couldn't find it. Oh well. It's still pretty cool.
Racing diesels fascinate me, but I don't know much about them.
And finally you have the wonderful Triumph 1500cc four cylinder, which produces a mighty 63 hp and is "rather agricultural" as the old British announcer on NBC Sports racing coverage might say. It sounds like half a Mustang and it really doesn't matter because the car is either making me happy in cornering or making me sad by sitting there not running and neither way really has much to do with the engine power.
That's all I've got. Someone tell me about some weird and wonderful motors. I need a breath of automotive fresh air after this Trump shit.
They are cool though. It's been a while, but as I understand it the VR6 was even a little weirder than just a very narrow-angle V6. The cylinders were staggered and the two banks were close enough together to share a cylinder head. VAG made a W12 and also a W16, which they put in the Bugatti Veyron. The W12 was basically two VR6s, as you say, and the W16 was a "stretched" version, so basically two "VR8" motors, if such a thing existed. (Damn, I'd have liked to have a VR8!) I guess Lil Wayne's description of "two V8s, ain't no such thing as driving calm in this Bugatti" wasn't 
