Drupal - Creating an API without losing your soul.

Drupal services https://drupal.org/project/services is a one stock module for exposing every aspect of a drupal site's functionality as a service for multiple device consumption.
Services views module https://drupal.org/project/services_views enables site builders to expose their views (Drupal query builder) as a service making a developer build an entire API without writing a single line of code. If a developer wants custom service endpoints, they just create a module and use hook_services_resources() to get that endpoint up.
Other devices can now make requests and push content or fetch content to the API. All the authentication methods are also supported. Session authentication exists by default but turned off. A developer can enable that or use http basic authentication https://drupal.org/project/services_basic_auth or Oauth authentication https://drupal.org/project/oauth .