xTuple ERP is a family of ERP, CRM and accounting applications built on a core of open source software.
PostBooks Edition (PostBooks) is our free open source ERP solution for small to medium sized businesses. Built with the open source PostgreSQL database, and the open source Qt framework for C++, it provides the ultimate in power and flexibility for a range of businesses and industries.
PostBooks runs equally well on Windows, Linux, and Mac - and it's fully internationalized (multi-currency, support for multiple tax structures, and multilingual translation packs maintained by our global community)
xTuple ERP Standard Edition and OpenMFG Edition include additional features but require a commercial license from xTuple.