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.

Odoo - An all-integrated business app suite to unleash your growth potential.

ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.

Epicor Kinetic - Epicor ERP is a global enterprise resource planning solution.

Elorus - A super-easy online invoicing & time tracking software

Adempiere - ADempiere is a commons-based peer-production of Open Source ERP Applications.