I have a genuine fascination with things like this, things that have no right to exist and yet do. Their value at the time was questionable, much like dionb has already stated, however the engineering and "just cause we could" philosophy behind them is pretty cool.
Somewhat recently, ASRock made an x299 mITX board that's just insane once you start thinking about it and taking a closer look. Behold: https://www.asrock.com/mb/Intel/X299E-ITXac/index.asp
Very limited use cases, but fucking hell this is a thing of beauty. Now, if only they made a Threadripper board like that ... 🤣