Quintype - Data-driven publishing platform for digital content creators
Contentful - You don't need another CMS. You need a better way to manage content — unified, structured, and ready to deploy to any digital channel.
GraphCMS - The GraphQL Headless CMS
Gentics Mesh - Open source headless CMS, complete with multilanguage support, versioning and roles & permissions
Butter CMS - API-first CMS + blog platform built for developers & marketers.
Prismic - prismic.io is a web software you can use to manage content in any kind of website or app. API-driven.