CREST 
CREST (Carbon REST) is a RESTful hypermedia HTTP API that enables read and write access to parts of the EVE universe.
Resources
Things in the EVE universe are exposed as addressable resources with a canonical URI. A representation of a resource can be obtained by making an HTTP GET request to the resource URI. Resources may be updated by making PUT requests to their URI and removed by making DELETE requests to their URI.
All resources are reachable from the root API entry point URI. Clients should not construct URIs, but instead follow URIs included in representations they have received. URIs may be stored as bookmarks, shared in IMs, sent as emails and published on web sites. CCP will endevour to support URIs as permalinks, but client applications should be able to cope with URIs becoming invalid as the API evolves and resources may be served from different locations just as web browsers cope with broken links.
Representations
Resources are represented as hypermedia documents which link to related resources. The structure of representations are described by media types. Clients specify the representation they would like to received using the Accept header of their request and specify which representations they are sending in the Content-Type header.
Representations may be extended to add new relationships and functionality, so clients must ignore all extra data they receive. Representations will never rename or remove attributes.
Where renaming or removing attributes is required to support new functionality, a new version of the representation will be defined as a new media type and the old representation will continue to be supported for as long as possible. The newest version of a representation will be served by default to ensure that new clients are developed using the newest representations. Clients that are widely distributed and not automatically updated should always supply Accept headers if they rely on the structure of representations.
Representations are formatted as JSON objects containing name/value pairs and nested objects and arrays. Some name/value pairs are optional, meaning that they may be omitted by senders when not applicable. Some name/value pairs have default values which will be used when a value is not provided.
The structure of all representations used by the CREST API are described below in human readable HTML and machine readable JSON schema formats. The schemas and documentation are generated nightly by a spider making OPTIONS requests to the self-describing CREST API.
Authorization
Requests to non-public parts of the API are made on behalf of a character. Client applications are further restricted by the set of scopes a player has allowed the application to use on behalf of a character. When making a request to a non-public part of the API, client applications must supply an OAuth 2 token granted by login.eveonline.com in the Authorization header. If the character is not allowed to make the request, or the token does not have the correct scopes, the request will be denied.
Localization
Clients may specify the languages they would like to receive responses in by providing the Accept-Language header with their requests.
Examples
An example JavaScript client that demonstrates how to use CREST can be found here http://jimpurbrick.com/contactjs. The open source code for the example client is available here https://github.com/jimpurbrick/contactjs.
crestexplorer is a similar JavaScript client which allows the CREST API to be explored and URLs to nicely rendered views of resources to be shared. The open source code can be found here https://github.com/jimpurbrick/crestexplorerjs.
crestschema is a JavaScript library which converts the descriptions of representations returned by OPTIONS requests made to CREST resources in to JSON schemas. The schemas can then either be used to generate client code, or crestschema can be used directly by JavaScript clients to generate and validate schemas dynamically.
Information
Presentations describing the design and use of CREST can be found here and here. Official CCP developer resources can be found here.