In the 1970's, Mike Rutherford (Genesis) played one of the coolest instruments I have ever seen. I was a double necked guitar/bass. The top half was a Rickenbacker 12-string electric guitar (think Roger McGuinn and R.E.M.) and the bottom half was a Ric 4003 bass (Chris Squire of Yes was the King of snarly Ric in my book).
This instrument is a one-of-a-kind; they don't make these at the factory. Rutherford had it built for him. I came across a link tonight on Rik Resource documenting the re-creation of this instrument by William Young Guitars. If you are at all sensitive about seeing beautiful guitars and basses brutalized with power tools, brace yourself before clicking the link, but as you can see from the photo, the results are unbelievable.