Volto (https://github.com/plone/volto) is a React-based frontend for content management systems, currently supporting three backend implementations: Plone, Guillotina and a NodeJS reference implementation.
Plone (https://plone.org) is a CMS built on Python with more than 17 years of experience. Plone has very interesting features that are still appealing to developers and users alike as customizable content types, hierarchical URL object traversing and a granular permissions model that allows you to build from simple websites to complex huge intranets. Volto exposes all that features and communicates with Plone via its mature REST API. Volto has the ability of being highly themable and customizable.
Volto also supports other APIs like Guillotina (https://guillotina.io/), a Python resource management system, which is inspired on Plone using the same basic concepts like traversal, content types and permissions model.
Last but not least, it also supports an early Nodejs reference (https://github.com/plone/volto-reference-backend) API implementation that demos how other systems could also use Volto to display and create content through it.