Alpaca : Given a web API, Generate client libraries in node, php, python, ruby
HTTP API design : This guide describes a set of HTTP+JSON API design practices, originally extracted from work on the Heroku Platform API.
DevDocs : DevDocs combines multiple API documentations in a fast, organized, and searchable interface.
Swagger is a powerful open source framework backed by a large ecosystem of tools that helps you design, build, document, and consume your RESTful APIs.