Here's one from the Archives. I originally linked to this one back in the early days of this blog (the first English-language guitar blog and longest-running guitar blog ever, I hasten to add). I'm featuring this wonderful Flamingo Guitar again, because it's a favourite of mine and you may have missed it first time around.
In case you think I can't count, this guitar does indeed have five necks - mandolin, nylon string guitar, banjo, electric guitar and a Flamingo neck (of course!) and apparently it is fully playable. (That's a Bird of Paradise capo clamped to the banjo neck's 5th string machine head, by the way.)
It was built by luthier Bernard Lehmann, maker of fine acoustic and jazz guitars, as well as one or two oddities like this, two dreadnought guitars joined by one neck, a water-powered electric guitar, and a guitar that is part telephone. Wish I had photos of those!