Client Libraries 
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The API can be used from any application by sending basic HTTP requests; however, client libraries simplify the process of querying or creating specific resources. These libraries make it easy to connect an external application to the WordPress REST API using a variety of programming languages.
Alert: Aside from the Backbone.js client, these libraries are not part of WordPress core, and are not necessarily maintained or endorsed by the WordPress REST API team.
Note: To perform authenticated requests from outside of the WordPress admin, themes, or plugins, a separate authentication plugin is required.
JavaScript
The Backbone.js client is built in to WordPress core and provides Backbone.js models & collections for working with REST API resources.
node-wpapi is an isomorphic JavaScript client library for querying or writing to the REST API using an intuitive chaining syntax. It can be used with Node.js or with client-side JavaScript applications.
ember-wordpress provides a connection between Ember Data and the REST API
Ruby
wp-api-client: a read-only REST API client written in Ruby.
C# / .NET
WordPressPCL: a full REST API client written in C#.