BTCPay Server is an MIT-licensed, self-hosted Bitcoin payment processor with 0% platform cut and no third-party custody, bundling POS, donation buttons, pay links and crowdfunding, with Namecheap having processed over 73 million USD through it at the cost of running your own server and wallet security.
OpenNode is a Bitcoin-only payment processor offering on-chain and Lightning collection rails, per-transaction fiat conversion with locked rates, and roughly 1% standard processing fee per its official example.
Confirmo is a stablecoin-first payment platform founded in 2014, with 5 product lines spanning Checkout, Deposits, Payouts, Subscribe and Global Payroll, where Subscribe brings one-time authorization, automatic debits and cancellation into the stablecoin rail.