Haml is a layer on top of HTML or XML that is designed to express the structure of documents using indentation rather than closing tags. It was originally envisioned as a plugin for Ruby on Rails, but it can function as a stand-alone templating engine.

Mail is an internet library for Ruby that is designed to handle email generation, parsing and sending. The purpose of this library is to provide a single point of access to handle all email functions, including sending and receiving emails. All network type actions are done through proxy methods to Net::SMTP, Net::POP3 etc.

Mail has been designed with a very simple object oriented system that really opens up the email messages you are parsing, if you know what you are doing, you can fiddle with every last bit of your email directly.

Rack provides a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses, it unifies the API for web servers, web frameworks, and software in between into a single method call.

This package provides a Ruby implementation of RFC5869: HKDF. The goal of HKDF is to take some source key material and generate suitable cryptographic keys from it.

This Ruby library uses ANSI escape sequences to control the attributes of terminal output.

WEBrick is an HTTP server toolkit that can be configured as an HTTPS server, a proxy server, and a virtual-host server.

This library provides methods to read Adobe Font Metrics (afm) files and use the data therein.

This package provides a plugin for the RuboCop code style enforcing & linting tool for factory_bot files.

This gem is a library that provides trigonometric and transcendental functions for complex numbers. The functions in this module accept integers, floating-point numbers or complex numbers as arguments.

Coderay is a Ruby library that provides syntax highlighting for select languages.

Orderedhash is a Ruby library providing a hash implementation that preserves the order of items and features some array-like extensions.

OpenURI with transparent disk caching, which is useful to avoid making excessive queries, for example when scraping web pages.

This package provides a subclass of Object that includes the Comparable module for handling dates.

Ruby/Git is a Ruby library that can be used to create, read and manipulate Git repositories by wrapping system calls to the git binary.

Data URIs allow resources to be embedded inside a URI. The URI::Data class provides support for parsing these URIs using the normal URI.parse method.

The Listen gem listens to file modifications and notifies you about the changes.

This library provides a way to run code around tests in Minitest, written using either the unit test or spec style.

This gem provides parser dictionary data for AnyStyle.

This package provides a command line interface for running for Rack applications.

Byebug is a Ruby 2 debugger implemented using the Ruby 2 TracePoint C API for execution control and the Debug Inspector C API for call stack navigation. The core component provides support that front-ends can build on. It provides breakpoint handling and bindings for stack frames among other things and it comes with a command line interface.

Em-websocket is an EventMachine based WebSocket server implementation.

fog is a Ruby cloud services library. This package provides shared classes and tests for fog providers and services.

RubyProf is a fast code profiler for Ruby. Its features include:

Speed

Being a C extension, it is many times faster than the standard Ruby profiler.

Measurement Modes

It can measure program wall time, process time, object allocations and memory usage.

Reports

A variety of text and cross-referenced HTML reports can be generated.

Threads

Profiling multiple threads simultaneously is supported.

BRASS (Bare-Metal Ruby Assertion System Standard) is a basic foundational assertions framework for other assertion and test frameworks to make use of.