> The "custom" and "proprietary" are largely irrelevant, in that they're merely internal implementation details.

Agreed. I was merely trying to convey that they wouldn't be the normal [E]ATX form factor boards.

The parent was asking for something "off the shelf", and I took this to mean purchasing a motherboard by itself. You could get something like that from SM[0], but I doubt you'd be able to find a compatible chassis for the motherboard from anyone other than SM. At that point it probably makes more sense to just buy the system[1].

[0] http://www.supermicro.com/products/motherboard/Xeon/C600/X10...

[1] http://www.supermicro.com/products/system/2U/2048/SYS-2048U-...