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Stripe

Stripe is a comprehensive suite of payment APIs and financial services that enables businesses to accept online and in-person payments globally. It provides the robust tools necessary to handle credit cards, digital wallets, recurring billing, and complex marketplace payouts securely. Designed for developers and modern enterprises alike, Stripe streamlines financial operations by automating revenue management, fraud detection, and financial reporting. Its modular architecture allows companies to scale from simple checkout pages to fully customized global payment flows.

FastSpring

FastSpring is a payment processing and subscription billing platform built for companies selling software, SaaS, digital products, and games globally. As a merchant of record, it takes on responsibility for calculating and remitting sales tax and VAT across more than 200 regions and 35+ currencies, which removes a major compliance burden for companies expanding into new international markets. Beyond payments, it offers subscription and recurring billing management, a customizable localized checkout, fraud prevention tools, a built-in affiliate marketing network, and B2B sales quoting with e-signatures. FastSpring reports over 3,200 customers including Adobe, Intel, and Rovio, processing more than $2 billion in annual transactions, and provides REST APIs and webhooks for developers building custom purchase flows.

Lemon Squeezy

Lemon Squeezy is a merchant-of-record platform that handles payments, subscriptions, tax compliance and license key delivery for software sellers. It streamlines the entire checkout experience, letting developers focus on building products rather than managing financial logistics. The service offers built‑in tax calculation, automated license key generation, and robust subscription management, all delivered through a simple web dashboard and API. It integrates with major payment processors and popular developer tools to keep revenue flow smooth and compliant.

Polar.sh

Polar.sh is an open-source monetization platform that lets developers embed payments, subscriptions, and usage‑based billing directly into their software products. It provides a flexible API and ready‑made UI components to handle common billing scenarios without building a payment system from scratch. The platform supports popular payment gateways, offers self‑hosted and cloud‑hosted deployments, and includes tools for managing customers, invoices, and revenue analytics, making it ideal for indie developers and SaaS startups seeking a cost‑effective billing solution.