The best free alternative to SugarCRM is Odoo, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to SugarCRM and loads of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to SugarCRM are HubSpot (Freemium), EspoCRM (Freemium, Open Source), Bitrix24 (Freemium) and Mautic (Freemium, Open Source).
Build better eCommerce & business applications with the open-source Scipio ERP framework. From Accounting to Warehouse Management: a long list of business applications is available to you and waiting to be customized.
Zero BS CRM is a customer relationship manager built on WordPress. It lets you manage clients, invoices, customers, quotes, companies and ecommerce transactions (hooked into WooCommerce, PayPal). Built on the principle of keeping things super simple.