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.

Service Provider Pro - Client Portal Software. Productize your services and turn your agency into a profitable and scalable system.

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

MoonClerk - You're just 5 minutes away from accepting recurring payments and one-time payments online. Explore for Free. No credit card required.

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

Pabbly Subscriptions - Pabbly Subscription is a recurring billing & subscription management software.