Ruby on Rails is a full-stack web framework optimized for programmer happiness and sustainable productivity. It encourages beautiful code by favoring convention over configuration.
Rack provides a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call. Also see https://rack.github.io/.
Sinatra is a DSL for quickly creating web applications in Ruby with minimal effort.
Hanami is a web framework for Ruby
The Godfather of Sinatra provides a full-stack agnostic framework on top of Sinatra