I'm aware of the Xeon D line, but sadly that was also squarely aimed at the enterprise albeit maybe a smaller scale enterprise. It's not something you can easily go out and buy any more, and when you do it's both very expensive, still PC sized, and not any more power efficient at idle or configured TDP when compared to a new Intel workstation or new AMD setup.
EBay offers a number of Xeon D boards at reasonable prices, many with extensive passive cooling. They have a lot of life left in them, to my mind, with good enough power efficiency for a box with normally very low CPU load. No moving parts, nothing to break. Yes, they are not speed demons, but low TDP presumes that anyway. ECC RAM support is there, though.
