ERP products usually cost a fortune, but for small firms and startups, such high prices are unaffordable. But there are several opensource ERP products what are as good as expensive commercial ERP products.
webERP is a complete web based accounting/ERP system that requires only a web-browser and pdf reader to use. It has a wide range of features suitable for many businesses particularly distributed businesses in wholesale and distribution. It is developed as an open-source application and is available as a free download to use. The feature set is continually expanding as new businesses and developers adopt it.
Tryton is a three-tier high-level general purpose computer application platform on top of which is built a business solution (or ERP) through a set of so-called Tryton modules. The Tryton platform is organised around a three-tiers architecture: The Tryton client, the Tryton server and the DBMS (mainly PostgreSQL). The platform along with the official modules is licenced under the GPL-3.
SQL-Ledger is a double entry accounting system. Accounting data is stored in an SQL Database Server and a standard web browser can be used as its user interface. The system uses the Perl language with a database interface module for processing and PostgreSQL for data storage.
PostBooks is an open source accounting and enterprise resource planning business system geared toward small to medium sized businesses. It is released under a CPAL license and is thus free software. PostBooks is maintained as an open source project on SourceForge.net but is based on the commercially licensed xTuple ERP system created by xTuple, a private software company based in Norfolk, VA.