Sage Intacct - Intacct is a cloud-based accounting and financial management system that is designed for the businesses of all levels.
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
SolidInvoice - SolidInvoice is simple to use online invoicing software that helps small businesses to get paid faster on time.
Elorus - A super-easy online invoicing & time tracking software
Upodi - Unified Commerce Platform.
MinuteDock - Web-based time tracking software designed to integrate with the Xero accounting package.