Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.
flyceipts - A fresh look at digital receipts & other documents.
Recurly - Subscription billing and recurring billing management. Recurly offers enterprise-class subscription billing for thousands of companies worldwide.
Keep Your Friends Close - A free e-book about maximizing Customer Lifetime Value
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.
Ramp Receipts - Create a receipts/invoice dashboard for Stripe