PostBooks is the foundation of the xTuple ERP software developed and marketed by the company of the same name beginning in the year 2000.
[1] PostBooks is divided into 7 functional modules: Accounting, Sales, CRM, Manufacture, Purchase, Inventory and Products.
The PostBooks project includes two application interface options: a locally installed Graphical User Interface (GUI) client and a REST based web services API for integration with third-party applications, all of which feed into the same PostgreSQL back end database.
Both the Qt client and PostgreSQL database server may be run on Windows, Macintosh, or Linux operating systems.
One of the major advantages of the PostBooks (and commercial) software is the technology it is written in, which allows significant customization of the database and functionality of the system.
This is evident in that the entire Manufacturing feature set is developed as a scripted package over the commercial core application.