Although most major ERP vendors have been focusing on
selling multi-million dollar installations of their software to very large
organizations, it has begun shifting in focus as ERP vendors realize the
small-to-medium size business market is probably just as large. There are a large amount of ERP vendors depending on the size of the business. Some ERP
vendors that focus on small-to-medium sized businesses are open source or
cloud base ERP systems. An open source software is a software in which its
source code is made available by the copyright holder, and provides the rights
to study, change, and distribute the software to anyone. A
few open source ERP vendors I found were: Odoo, xTuple, Dolibarr, and ERP 5.
http://logistics.about.com/b/2010/05/26/erp-for-small-business.htm
http://en.wikipedia.org/wiki/Open-source_software
http://www.enterpriseappstoday.com/erp/10-open-source-erp-options.html