Rain is a gem to generate beautiful and customizable API documentation, inspired by yard and rdoc. The aim of Rain is to generate beautiful API documentation from a ruby comment syntax with markdown mixed in. The documentation can be inline in .rb files, or separate .md or .txt files for overall architecture documentation. Rain also allows a large amount of customization when it comes to templating and appearance of the API documentation. Branding and unity of documentation appearance is important and Rain offers a simple ERB-based template system.