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.
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
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
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.
MinuteDock - Web-based time tracking software designed to integrate with the Xero accounting package.
Braintree - An all-in-one solution to accept, process, and split payments in your mobile app or online - from small business to large enterprise.