Stripe - Online payment processing for internet businesses. Stripe is a suite of payment APIs that powers commerce for online businesses of all sizes. Use Stripe’s payment platform to accept and process payments online for easy-to-use commerce solutions.

Lago Billing - Open-source alternative to Stripe Billing and Chargebee

Recurly - Subscription billing and recurring billing management. Recurly offers enterprise-class subscription billing for thousands of companies worldwide.

Metronome - Metronome helps software companies launch, iterate, and scale their usage-based business models, with billing infrastructure that works at any size and stage.

ServiceBot - The new, open source way to run a business online. Subscription billing, Self-service customer portal, service lifecycle management?

Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.