DevDocs : DevDocs combines multiple API documentations in a fast, organized, and searchable interface.
Alpaca : Given a web API, Generate client libraries in node, php, python, ruby
ApiGen : ApiGen is the tool for creating professional API documentation from PHP source code, similar to discontinued phpDocumentor/phpDoc.
StyleDocco : StyleDocco generates documentation and style guide documents from your stylesheets.
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.