Odoo

The most established modular open-source ERP and CRM suite.

Odoo is a comprehensive open-source suite of business applications covering ERP, CRM, accounting, inventory, e-commerce, HR, manufacturing, and more, built primarily in Python with a PostgreSQL backend and its own ORM and web framework. Modules share a common data model and can be enabled independently. It is notable for its modular architecture and large ecosystem of community and official apps.