Speaking of APIs and documentation in the previous post:
Swagger is a specification and complete framework implementation for describing, producing, consuming, and visualizing RESTful web services.
Describe your API in a JSON file like this, and Swagger will turn it into that. Alternatively you can provide your project with Swagger Annotations and then run it through a parser (such as Swagger-PHP) to let it automatically generate the docs.
Related: Simple REST API Explorer, my attempt to quickly allow one to consume a RESTful/Hypermedia API.