Crow.app - Pricing and experimentation tools for Stripe
Receiptful - Receipts that increase CLTV. Exclusive (early access to PH)
Mailgun - A set of powerful APIs that enable you to send, receive and track email from your app effortlessly whether you use Python, Ruby, PHP, C#, Node.js or Java.
QuickReceipts - A mobile app that automatically tracks, organizes, and stores your digital receipts privately on your device.
Stripe for Gmail - Display customers Stripe information within inbound emails
Keep Your Friends Close - A free e-book about maximizing Customer Lifetime Value