Decoupling Drupal can be arduous, whether you’re developing a Drupal-backed front end or configuring Drupal to be an ideal content repository for decoupled applications.

In Drupal terms, Reservoir is a minimalist distribution for decoupling Drupal. In more general terms, Reservoir is a flexible and simple tool to build content repositories for any application to consume: it focuses on modeling content, managing content, and interacting with that content via HTTP APIs.

https://dev.acquia.com/blog/introducing-reservoir-a-distribution-for-decoupling-drupal/19/06/2017/18296