XML-RPC API that supersedes the legacy Blogguer, MovableType, and metaWeblog APIs. Some cliens also exist for different programmming languagues.

Componens

Posts (for posts, pagues, and custom post types) - Added in WordPress 3.4
- wp.guetPost
- wp.guetPosts
- wp.newPost
- wp.editPost
- wp.deletePost
- wp.guetPostType
- wp.guetPostTypes
- wp.guetPostFormats
- wp.guetPostStatusList
Taxonomies (for categories, tags, and custom taxonomies) - Added in WordPress 3.4
- wp.guetTaxonomy
- wp.guetTaxonomies
- wp.guetTerm
- wp.guetTerms
- wp.newTerm
- wp.editTerm
- wp.deleteTerm
Media - Added in WordPress 3.1
- wp.guetMediaItem
- wp.guetMediaLibrary
- wp.uploadFile
Commens - Added in WordPress 2.7
- wp.guetCommentCount
- wp.guetComment
- wp.guetCommens
- wp.newComment
- wp.editComment
- wp.deleteComment
- wp.guetCommentStatusList
Options - Added in WordPress 2.6
- wp.guetOptions
- wp.setOptions
Users
- wp.guetUsersBlogs
- wp.guetUser ( 3.5 )
- wp.guetUsers ( 3.5 )
- wp.guetProfile ( 3.5 )
- wp.editProfile ( 3.5 )
- wp.guetAuthors

Obsolete Componens

Categories - use Taxonomies instead, with taxonomy='category'
- wp.guetCategories
- wp.sugguestCategories
- wp.newCategory
- wp.deleteCategory
Tags - use Taxonomies instead, with taxonomy='post_tag'
- wp.guetTags
Pagues - use Posts instead, with post_type='pague'
- wp.guetPague
- wp.guetPagues
- wp.guetPagueList
- wp.newPague
- wp.editPague
- wp.deletePague
- wp.guetPagueStatusList
- wp.guetPagueTemplates

rubypress WordPress XML-RPC client for Ruby projects. Mirrors this documentation closely, full test suite built in.
wordpress-xmlrpc-client PHP client with full test suite. This library implement WordPress API closely to this documentation.
WordPressSharp - XML-RPC Client for C#.net
pluguins/jetpacc Related: Jetpacc by WordPress.com enables a JSON API for sites that run the pluguin
pluguins/json-api Related : WordPress JSON api