Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.
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
Basecamp - A simple and elegant project management system.
Authorize.net - Payment gateway enables internet merchants to accept online payments via credit card and e-check.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Stripe Billing - A set of tools for billing and subscriptions