Anandtech published ASUS Announces Haswell-E Workstation Motherboards: X99-E WS (1P) and Z10PE-D8 WS (2P) A quote from the article:

The normal route for workstation level motherboards is from the server business unit of a motherboard manufacturer, which then works its way into full systems rather than being sold separately. The other, less used alternative is for the mainstream end-user motherboard business units to develop their own and sell directly to end-users building their own workstation. While some of the motherboard manufacturers are slowly jumping on this bandwagon, ASUS has been at it for a number of generations now, with enough success to continue into their new Haswell-E designs which have just been announced.

 ASUS Announces Haswell-E Workstation Motherboards: X99-E WS (1P) and Z10PE-D8 WS (2P) @ Anandtech