ProcessWire is an open-source CMS released in 2010 and built on PHP, known for its flexible field model, API-driven development and template freedom, with 20+ built-in field types under the MPL 2.0 license, a common choice for developers building custom websites and business systems.
Cockpit CMS is an open-source headless content management system released in 2015 under the MIT license, delivering JSON content through a REST API. It is lightweight, self-hostable and flexible for developer-driven, tech-stack-agnostic content backends.
Agnostic CMS is an open-source headless content management system created by Tom H. in 2020, built around GraphQL API with custom content modeling and multi-environment deployment, self-hostable at zero license cost.
Brink CMS, founded in 2018 by Chris B. and headquartered in Sweden, is a headless content management system designed for static websites, offering an API-driven content management experience.