Odoo - An all-integrated business app suite to unleash your growth potential.
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.
Infor ERP - An ERP suite for the manufacturing & distribution industries
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
Adempiere - ADempiere is a commons-based peer-production of Open Source ERP Applications.
Elorus - A super-easy online invoicing & time tracking software