What are the really unusual or weird computers?

I never cease to be amazed by the level and depth of knowledge of obscure machines on this list. Knowledgeable discussions of machines I've never even heard of in 20y in the business and a good while longer as a hobbyist. So I thought I'd ask a question on a slightly different tack. What are the most bizarre, way-out or just plain *different* machines that folks have seen? The basic von Neumann computer is well-established, but most of them have a lot more common ground than that. Uniquely-identified disks, an OS with a command line that lets you create, rename, execute, edit and delete files on those disks. Maybe graphics. Maybe dumb terminals. Maybe a teletype. But set aside the cosmetic differences, they are, to a large degree, much of a muchness. From a PDP/11 to a VAX to MS-DOS, the actual overall CLI experience is very similar. Unix is a bit different - cryptic commands, one big virtual directory tree - but it's really more of the same underneath. The Mac was pretty different when it was new: no CLI at all, for example. Otherwise, though, it's not that remarkable. But I keep reading about Lisp machines. No good general-purpose introduction for the interested computer-literate reader who's never seen one and doesn't speak Lisp, though, but from what I've read, they sound unique. The Canon Cat had a unique UI as well, from what I've seen. What else was there? What other machines - general-purpose desktop (or desk-side or whatever) computers were there that Thought Differently? I'm not really thinking of embedded systems and the like here, but thinks you sat in front of and worked upon.