pERP is an eGroupWare ERP Group of Modules, mostly geared towards manufacturing, but very configurable. It requires eGroupWare v1.5+ and PHP 5.2+.
Full requirements at http://www.projecterp.org/mediawiki/index.php/Installation

There is currently support for:

• Fine ACL
• basic accrual accounting
• Suppliers with catalogs
• Multiple stock and manufacturing locations,
• Bill of Materials

Of note is the integration into eGroupWare:

• Home page bits for Accounts Payable and Receivable
• Addresses for Users, Suppliers & Clients are stored in the addressboook
• Most parts support linking, and some parts link automatically.