Zammad is a web based open source helpdesk/customer support system with many features to manage customer communication via several channels like telephone, facebook, twitter, chat and e-mails.

Odoo is business management software including CRM, e-commerce, billing, accounting, manufacturing, warehouse, project management, and inventory management.

ERPNext is a free and open-source integrated Enterprise Resource Planning software. It is a generic ERP software used by manufacturers, distributors and services companies.

VTiger is a cloud-based CRM that enables businesses to deliver customer experiences by breaking barriers between their marketing, sales, and support teams.

Helpy is an open source customer support platform designed for companies which take care of customer data security and control

SugarCRM is an open source customer relationship management system with following functionalities - marketing campaigns, sales-force automation, customer support, collaboration, Mobile CRM, Social CRM and reporting.

Sentrifugo is a free and powerful new-age Human Resource Management System that can be easily configured to adapted to organizational processes. It features HR, leave mngt, time mngt, acquisitions, analytics and other functionalities.