marcel provides MIME type detection using magic numbers, filenames, and extensions

ActionMailbox receives and processes incoming emails in Rails applications.

Provides Sprockets implementation for the Rails Asset Pipeline.

Turbo aims to be as fast as single-page web application without having to write any JavaScript. Turbo accelerates links and form submissions without requiring server-side changes to the generated HTML. It allows carving up a page into independent frames, which can be lazy-loaded and operated as independent components. Finally, it helps making partial page updates using just HTML and a set of CRUD-like container tags. These three techniques reduce the amount of custom JavaScript that many web applications need to write by an order of magnitude. And for the few dynamic bits that are left, Stimulus can be used.

ActiveSupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. It includes support for multibyte strings, internationalization, time zones, and testing.

Propshaft is an asset pipeline library for Rails. It's built for an era where bundling assets to save on HTTP connections is no longer urgent, where JavaScript and CSS are either compiled by dedicated Node.js bundlers or served directly to the browsers, and where increases in bandwidth have made the need for minification less pressing. These factors allow for a dramatically simpler and faster asset pipeline compared to previous options, like Sprockets.

This gem is used to handle HTML sanitization in Rails applications. If you need similar functionality in non Rails apps consider using Loofah directly.

The With advisory lock gem adds advisory locking to ActiveRecord for PostgreSQL and MySQL. SQLite is also supported, but this uses the file system for locks.

This library integrates the SASS stylesheet language into Ruby on Rails.

ActionView provides conventions and helpers for building web pages in Ruby.

Active Record connects classes to relational database table to establish an almost zero-configuration persistence layer for applications.

This package provides a Ruby wrapper for the MRI 2.0 debug_inspector API.

Import maps can import JavaScript modules using logical names that map to versioned/digested files -- directly from the browser. It makes it possible to build modern JavaScript applications using JavaScript libraries made for ES modules (ESM) without the need for transpiling or bundling, which removes the need for Webpack, Yarn, npm, or any other part of the JavaScript toolchain. All that is needed is the asset pipeline that is already included in Rails.

ActiveJob allows declaring job classes in a common way across Rails applications.

ActionPack provides conventions for building and testing MVC web applications. These work with any Rack-compatible server.

Compose, deliver, receive, and test emails using the controller/view pattern. Including support for multipart email and attachments.

GlobalID provides a way to generate URIs from a model in Ruby that uniquely identify it.

Bootsnap is a library that plugs into Ruby, with optional support for YAML, to optimize and cache expensive computations.

ActionText edits and displays rich text in Rails applications.

Spring is a Ruby on Rails application preloader. It speeds up development by keeping your application running in the background so the application does need to boot it every time you run a test, rake task or migration.

ActiveStorage integrates file storage services with Rails applications, allowing files to be attached to ActiveRecord models.

Action Cable integrates WebSockets with Rails applications. Through WebSockets it allows for real-time features in web applications.

This gem provides Ruby and Ruby on Rails integration with Autoprefixer, which can parse CSS and add vendor prefixes to CSS rules using values from the Can I Use website.

This package provides support for using RSpec to test Ruby on Rails applications, in pace of the default Minitest testing library.