HelpGuides was built for technical teams that need to publish end user documentation. However, it also supports publishing API documentation for REST-based APIs.
When creating documentation for an API end point you can use the article type to format content as a REST end point in your user documentation.
For example, DailyStory's REST API documentation:
When selecting the article type for a new document select API Reference. This will add the ability to specify the HTTP verb, e.g. GET, PUT, POST, etc., as well as the endpoint's URL.
The HTTP verb is shown in the lefthand menu and is shown when viewing the documentation.
The REST API widget is a special widget only available for articles that are set to type API Reference. This widget examines properties of the article, such as the HTPP verb and path to render options for documenting a REST end point.