CoinPayments - Payment gateway providing buy now buttons, shopping carts, and more to accept Bitcoin, Litecoin, and other cryptocurrencies/altcoins on your website/online store.
BTCPay Server - A free and open source server for merchants wanting to accept Bitcoin for their business.
CoinGate - CoinGate is a payment gateway for Bitcoin, XRP, Litecoin, Ethereum and 50 other cryptocurrencies.
BitPay - Bitcoin payment gateway. Enterprise-grade solutions, from the pioneer of bitcoin payments.
ALFAcoins - A secure payment gateway for cryptocurrencies
NOWPayments - NOWPayments is a crypto payment gateway that supports more than 250 cryptocurrencies, including fiat, and offers simple tools to accept crypto payments, like a crypto API, plugins, invoices.