Grape is a REST-like API micro-framework for Ruby. It's designed to run on Rack or complement existing web application frameworks such as Rails and Sinatra by providing a simple DSL to easily develop RESTful APIs. It has built-in support for common conventions, including multiple formats, subdomain/prefix restriction, content negotiation, versioning and much more.
Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design.
Flask is intended for getting started very quickly and was developed with best intentions in mind.
Sinatra is a DSL for quickly creating web applications in Ruby with minimal effort.
Rails is a web-application framework that includes everything needed to create database-backed web applications according to the Model-View-Controller (MVC) pattern.