ERP5 is a full featured ERP with a very flexible architecture designed to fit any business process. ERP5's functional design is based on 5 types of documents: orders, deliveries, accounting documents, CRM documents and PDM documents.
Orders are used to define what a customer wants to buy (Sale Order) and under which conditions (Sale Trade Condition) the transaction will take place. They are also used to define what a company wants to buy from a supplier (Purchase Order) and under which conditions (Purchase Trade Condition) the transaction will take place. Orders can also represent intangible requests such as Tasks.
Deliveries are used to define what a company is shipping to its customers (Sale Packing List), what the company is receiving from a supplier (Purchase Packing List) and what is planned for consumtion during production (Production Packing List). Deliveries can also represent intangibles such as Task Reports used in project management.
Accounting documents represent the transfer of the property of goods or services which have been shipped to customers (Sale Invoice) or received from suppliers (Purchase Invoice). Accounting documents also provide for general ledger accounting.
CRM documents keep track of customer releations in a purely documentary way.
PDM documents such as Transformations (a.k.a. BOM) define how a product can be produced from its individual components.
Multiple documents can be combined into a complex business process such as ordering, procurement, CRM, etc.