Contentful is one of the most prominent headless CMSs at the moment. As such it provides you all the content management capabilities of traditional tools like WordPress while decoupling the delivery of this content via an API that can be used to retrieve content.
Headless CMS are quickly turning from the new kid on the block intro everyone's favourite. And I totally understand why: it makes thinking about building a frontend so much easier, for once you actually know what is happening and we have great separation of concerns. For me as a webdev this is great stuff!