SuiteCRM

SuiteCRM is the most mature open source CRM available. Originally forked from SugarCRM when Sugar went closed source, it now ships under AGPLv3 with a full sales pipeline, contact management, marketing automation, and reporting stack. Salesagility (the maintainers) released version 7.15.1 this March, and the repo shows nearly 17,000 commits and 230 releases. This isn't a hobby project.

Self-hosting is the standard LAMP-ish stack: PHP 8.1 through 8.4, Apache (recommended) or IIS, and MySQL/MariaDB or SQL Server. Plan a few hours for a clean install and ongoing time for patches. The customization surface is large; SuiteCRM accommodates everything from solo consultants tracking deals to mid-market companies running full sales operations.

Solo and small teams: self-host. The savings versus Salesforce at any team size are real, and the data stays yours. Large teams with limited PHP ops capacity: SuiteCRM Hosted (the official managed offering) plus SuiteASSURED support is the practical path. Enterprise teams currently on Salesforce: this is a real migration. Possible, but multi-quarter.

The catch: the UI looks like 2015. The data model and features are competitive, but the interface is dated next to HubSpot or modern CRMs like Attio. If your sales team cares about the look as much as the function, factor that in.