For a while now Ryan has been the driving force behind an exciting project to create an API for WP core. The WordPress REST API team are aiming for inclusion in 4.1 so they really have their work cut out for them at the moment. Human Made are right behind the project and Ryan is currently having a day each week to focus time and energy on it. The API should have a significant impact for developers in the future by extending the range and scope of what they can create for WordPress.
The API gives developers the power to access data from posts, media, users, and more, through an easy-to-use interface. This will give developers the ability to create a new class of applications and tools for WordPress, including more powerful mobile applications, more fluent web applications, and easier to use developer tools.
JSON is a widely popular standard for exchanging data on the web, and is supported by practically every programming language in popular use. The API combines this with the concept of REST, which uses the full extent of the HTTP standard powering the web, to provide a powerful way to access and modify WordPress data.
Check out the WordPress REST API team site for more information and join the team.