Odoo (formerly OpenERP) is a suite of open-source business apps written in Python and distributed under the AGPL license, under the Open Core software business model. It is used by 2 million users worldwide to manage companies of all size.
Odoo vs SAP Business Suite opinions
I think Odoo used to be good in the past when it was "really" free and fully featured, but now it cannot be used really in the context of fully featured free open-source.
ERPNext is a free and open-source integrated Enterprise Resource Planning (ERP) software developed by Frappé Technologies Pvt. Ltd. and is built on MariaDB database system using a Python based server-side framework.
ERPNext vs SAP Business Suite opinions
Dolibarr ERP & CRM is a modern and easy to use open-source web software package to manage your business (customers, invoices, orders, products, stocks, agenda, e-mailings, shipments...).
Bitrix24 is a collaboration software with complete tools for management, collaboration, communication, and sales. Bitrix24 gives you a unified platform for your files, projects, messages, tasks, and contacts.
Crust CRM is a 100% free and open-source CRM. It's fully featured and includes rich dashboards, automation rules (workflows), collaborative team messaging and much more. You can customise your CRM with the included low-code development platform.
Mautic is marketing automation software (email, social, & more). Install on your own website or create a free hosted account. The simple 3-step setup process takes less than 5 minutes and you'll be ready to reclaim control of your marketing.
Web-based CRM for sales, service, marketing, and call center operations that allows users to manage customer relationships and customer satisfaction.
SuiteCRM provides an enterprise-grade Customer Relationship Management (CRM) application to a global community of users and software developers. It is a robust and credible alternative to Salesforce, Microsoft and the major CRM vendors.This app doesn't have any features at the moment.
Tryton is a three-tiers high-level general purpose application platform under the license GPL-3 written in Python and uses PostgreSQL as database engine. It's the core base of a business solution providing modularity, scalability and security.