Odoo is a CRM open source software that has extensible architecture and integrations with 10,000+ apps. It has an excellent contact management feature which makes it a great option for retail, restaurants, or other brick-and-mortar enterprises. It has advanced inventory management, email marketing, and sales operations features. 

It has features for projects, websites, invoicing, eCommerce, wireless support, accounting, employees, inventory, manufacturing, documents, spreadsheets, partners, etc. It is highly scalable and cost-effective