Zoho Invoice - 100% free online invoicing software for small businesses.
Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.
FreshBooks - The ideal accounting software for small business owners.
Recurly - Subscription billing and recurring billing management. Recurly offers enterprise-class subscription billing for thousands of companies worldwide.
Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
Zuora - Zuora creates cloud-based software on a subscription basis that enables any company in any industry to successfully launch, manage, and transform into a subscription business.