Fractal Design Define Nano S ITX -> ATX modification.
Very nice looking and small enough case, but it's only for ITX mobo's. After a bit of dremeling, there's an ATX motherboard, 3.5" hot-swap HDD bay and vibration absorbing HDD cage. The back plate is made of 1.5mm aluminium sheet and the ATX sized mobo tray is taken from Yariko's full ATX case (thanks!).
More details: http://operationalsmoke.blogspot.com/2016/06/case-mod-fractal-design-define-nano-s.html