Openbravo is "Everyone's ERP"--a comprehensive, ready to use, web-based open source business management solution that automates all of the core business processes for small and medium-sized companies, ranging from accounting and financial management, to sales, purchasing, inventory management and more.

Learn more about Openbravo ERP in http://www.openbravo.com/product/erp/

This project offers Ubuntu users a PPA with packages of the latest Openbravo ERP releases:
https://launchpad.net/~openbravo-isv/+archive/ppa