BillGrid.com - BillGrid is an easy to use online invoicing, billing and expense management system that will save you time with tracking clients projects, expenses, invoices and payments.
Postman - The Collaboration Platform for API Development
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
Cdyne - Cdyne is a professional REST and SOAP API provider.
fusebill - Fusebill is the leading recurring billing and subscription management software for businesses. Try Fusebill for subscription billing made easy!
LinkedIn - LinkedIn is a business-oriented social networking service, mainly used for professional networking.