Stripe

Stripe lets businesses accept payments online and in person and manage the money that follows. Its APIs and prebuilt pieces, such as Checkout and Payment Links, take cards, wallets and many local payment methods, and Billing handles subscriptions and invoicing.

Around that sit tools for fraud prevention (Radar), tax calculation, revenue reporting, and payouts for marketplaces and platforms (Connect). Developers know it for its documentation and test mode, which lets you build a full payment flow before going live. Pricing is per transaction, with no monthly fee on the standard plan.