This crypto-mining Asus motherboard supports 20 GPUs, because 19 wasn't enough - CNET
BTC-S37 Mining Motherboard Set, with CPU 128GB MSATA SSD and 8GB Memory DDR3 8 GPU Mining Motherboard Kit, Compatible with Bitcoin Eth and other multi-currency mining - Newegg.com
Amazon.com: SHANGZHAOYUAN B250 BTC-12P Mining Motherboard (Intel 6th/7th Gen) LGA 1151 Motherboard with 12 PCIe Slots, VGA+DVI, MSATA, 2*DDR4, USB 3.0 for Miner (BTC/ETH/ZEC/ETC) : Electronics
Amazon.com: H510 PRO BTC+ LGA1200 1DDR4 : Electronics