Killbill - Open-Source Subscription Billing and Payment Platform
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.
Muni-Link - Cloud-based utility billing software
Recurring Payments - No need to create invoices. No need to remind clients to pay
Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.
TillyPay - Recurring & single payment links, powered by Stripe.