Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.
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.
Quiken - All-in-one client and request management platform.
Killbill - Open-Source Subscription Billing and Payment Platform
Stripe Billing - A set of tools for billing and subscriptions
SlimPay - Payments for subscriptions