swagger.io - Swagger is an open source RESTapi Documentation Tool.
PayPal - PayPal is the faster, safer way to pay online without sharing financial details, send and receive money or accept credit and debit cards as a seller
Link to QR - Free beautiful QR codes
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.
Slate API Docs Generator - Create beautiful, intelligent, responsive API documentation.
Payoneer - Whether making international payments, receiving funds, managing your digital business, or accessing capital, Payoneer opens your business up to the world.