For any enterprise that needs to implement an ERP system, the basic modules that are essential would include all the major functions of the enterprise that describe it completely.

OpenERP is one such system that does it all and has all the modules to cater such requirements and even more, but talking about main modules, these modules are always required and should always be installed. Some of the major and very important modules are:

1. account: this module is responsible for accounting and financial management. It covers:

General accountings

Cost / Analytic accounting

Third party accounting

Taxes management

Budgets

Customer and Supplier Invoices

Bank statements

Reconciliation process by partner

Other modules like account_accountant manages all the journal entries, account_voucher manages payments and depend on account module.

2. sale: this module manages all the sales related tasks. It covers:

Quotations to Sales Order

Sales Order to Invoice

Invoicing methods: invoice on orders, delivery, time-sheets, and advance invoice

Products and prices

3. point_of_sale: manages a quick sale process. It covers:

Allow payment mode and split one payment mode into multiple

Compute money to return

Create and confirm picking lists

Create quick invoices and refunds.

4. stock: this module manages all the inventory and inventory related functions, can even manage multi-warehouses and multi-locations. It covers:

Moves history and planning

Inventory methods

Stock valuation like standard or average price

Automatic reordering rules as stock level, JIT

Bar code support

Detection of mistakes through double entry system

Traceability as upstream/downstream, production lots, serial number

5. purchase: this module manages all the purchases for goods from the supplier.

6. mrp: this module manages the manufacturing process. It covers:

Make to Stock / Make to Order (by line)

Multi-level BoMs

Multi-level routing

Scheduler computation periodically / Just In Time module

Different reordering policies

Costing method by product: standard price, average price

7. crm: this module manages customer relationship. This module manages:

leads, opportunities, meeting, phonecall etc

communication, identification, prioritization, assignment, resolution and notification.

ensures cases successfully tracked by users, customers and suppliers

send reminders, process the requests automatically

8. hr: this module manages all the human resources. This module manages employees and employee hierarchy, the hr department, and hr jobs. Though we have other modules that depend on this module like hr_attendance, hr_payroll, hr_holiday, hr_payroll_account, hr_recruitment, hr_evaluation. These can be installed as per your requirement.