Killbill - Open-Source Subscription Billing and Payment Platform
Recurring Payments - No need to create invoices. No need to remind clients to pay
Subscription Billing - Sales Order Processing that automates and manages cyclical and subscription based billings by generating invoices, quotes or orders in Dynamics GP.
TillyPay - Recurring & single payment links, powered by Stripe.
Trexle - Payment Platform Supporting One-time and Recurring Billing
Pabbly Subscriptions - Pabbly Subscription is a recurring billing & subscription management software.