| Abbrev | lib | 
| Calculates a set of unique abbreviations for a given set of strings | 
 | Base64 | lib | 
| Support for encoding and decoding binary data using a Base64 representation | 
 | Benchmark | lib | 
| Provides methods to measure and report the time used to execute code | 
 | BigDecimal | ext | 
| Provides arbitrary-precision floating point decimal arithmetic | 
 | Bundler | lib | 
| The best way to manage your application's dependencies | 
 | CGI | lib | 
| Support for the Common Gateway Interface protocol | 
 | CMath | lib | 
| Provides Trigonometric and Transcendental functions for complex numbers | 
 | Coverage | ext | 
| Provides coverage measurement for Ruby | 
 | CSV | lib | 
| Provides an interface to read and write CSV files and data | 
 | Date | ext | 
| A subclass of Object includes Comparable module for handling dates | 
 | DBM | ext | 
| Provides a wrapper for the UNIX-style Database Manager Library | 
 | DEBUGGER__ | lib | 
| Debugging functionality for Ruby | 
 | Delegator | lib | 
| Provides three abilities to delegate method calls to an object | 
 | DidYouMean | gem | 
| The gem that has been saving people from typos since 2014. | 
 | Digest | ext | 
| Provides a framework for message digest libraries | 
 | DRb | lib | 
| Distributed object system for Ruby | 
 | Exception2MessageMapper | lib | 
| Module for defining custom exceptions with specific messages | 
 | English | lib | 
| Require 'English.rb' to reference global variables with less cryptic names | 
 | ERB | lib | 
| An easy to use but powerful templating system for Ruby | 
 | Etc | ext | 
| Provides access to information typically stored in UNIX /etc directory | 
 | Fcntl | ext | 
| Loads constants defined in the OS fcntl.h C header file | 
 | Fiddle | ext | 
| A libffi wrapper for Ruby | 
 | FileUtils | lib | 
| Several file utility methods for copying, moving, removing, etc | 
 | Find | lib | 
| This module supports top-down traversal of a set of file paths | 
 | Forwardable | lib | 
| Provides delegation of specified methods to a designated object | 
 | GDBM | ext | 
| Ruby extension for the GNU dbm (gdbm) library | 
 | GetoptLong | lib | 
| Parse command line options similar to the GNU C getopt_long() | 
 | IO | ext | 
| Extension for Ruby IO class, .console | 
 | IO | ext | 
| Extension for Ruby IO class, #nonblock & #nonblock= | 
 | IO | ext | 
| Extension for Ruby IO class, #wait_readable & #wait_writable | 
 | IPAddr | lib | 
| Provides methods to manipulate IPv4 and IPv6 IP addresses | 
 | IRB | lib | 
| Interactive Ruby command-line tool for REPL (Read Eval Print Loop) | 
 | JSON | ext | 
| Implements Javascript Object Notation for Ruby | 
 | Logger | lib | 
| Provides a simple logging utility for outputing messages | 
 | Matrix | lib | 
| Represents a mathematical matrix. | 
 |  | gem | 
| minitest provides a complete suite of testing facilities supporting TDD, BDD, mocking, and benchmarking. | 
 | MakeMakefile | lib | 
| Module used to generate a Makefile for C extensions | 
 | Monitor | lib | 
| Provides an object or module to use safely by more than one thread | 
 | Mutex_m | lib | 
| Mixin to extend objects to be handled like a Mutex | 
 | Net::Telnet | gem | 
| Provides telnet client functionality. | 
 | Net::FTP | lib | 
| File Transfer Protocol | 
 | Net::HTTP | lib | 
| Hypertext Transfer Protocol | 
 | Net::IMAP | lib | 
| Internet Message Access Protocol | 
 | Net::POP3 | lib | 
| Post Office Protocol | 
 | Net::Protocol | lib | 
| Internal Protocol Class | 
 | Net::SMTP | lib | 
| Simple Mail Transfer Protocol | 
 | NKF | ext | 
| Ruby extension for Network Kanji Filter | 
 | ObjectSpace | ext | 
| Extends ObjectSpace module to add methods for internal statistics | 
 | Observable | lib | 
| Provides a mechanism for publish / subscribe pattern in Ruby | 
 | OpenURI | lib | 
| An easy-to-use wrapper for Net::HTTP, Net::HTTPS and Net::FTP | 
 | Open3 | lib | 
| Provides access to stdin, stdout and stderr when running other programs | 
 | OpenSSL | ext | 
| Provides SSL, TSL and general purpose cryptography for Ruby | 
 | OptionParser | lib | 
| Ruby-oriented class for command-line option analysis | 
 | OpenStruct | lib | 
| Class to build custom data structures, similar to a Hash | 
 | Pathname | ext | 
| Representation of the name of a file or directory on the filesystem | 
 | PowerAssert | gem | 
| Power Assert shows each value of variables and method calls in the expression. | 
 | PP | lib | 
| Provides a PrettyPrinter for Ruby objects | 
 | PrettyPrint | lib | 
| Implements a pretty printing algorithm for readable structure | 
 | Prime | lib | 
| Prime numbers and factorization library | 
 |  | lib | 
| Runs the Ruby Profiler__.  See profiler | 
 | Profiler__ | lib | 
| Provides a way to profile your Ruby application | 
 | PStore | lib | 
| Implements a file based persistence mechanism based on a Hash | 
 | Psych | ext | 
| A YAML parser and emitter for Ruby | 
 | PTY | ext | 
| Creates and manages pseudo terminals | 
 | Racc | ext | 
|   | 
 | Racc | lib | 
| A LALR(1) parser generator written in Ruby | 
 | Rake | gem | 
| Rake is a Make-like program implemented in Ruby. | 
 | RDoc | lib | 
| Produces HTML and command-line documentation for Ruby | 
 | Readline | ext | 
| Provides an interface for GNU Readline and Edit Line (libedit) | 
 | Resolv | lib | 
| Thread-aware DNS resolver library in Ruby | 
 |  | lib | 
| Replace Socket DNS with Resolv | 
 | REXML | lib | 
| An XML toolkit for Ruby | 
 | Rinda | lib | 
| The Linda distributed computing paradigm in Ruby | 
 | Ripper | ext | 
| Provides an interface for parsing Ruby programs into S-expressions | 
 | RSS | lib | 
| Family of libraries that support various formats of XML feeds | 
 | Gem | lib | 
| Package management framework for Ruby | 
 | Scanf | lib | 
| A Ruby implementation of the C function scanf(3) | 
 | SDBM | ext | 
| A simple file-based key-value store for String keys and values. | 
 | SecureRandom | lib | 
| Interface for secure random number generator | 
 | Set | lib | 
| Provides a class to deal with collections of unordered, unique values | 
 | Shell | lib | 
| An idiomatic Ruby interface for common UNIX shell commands | 
 | Shellwords | lib | 
| Manipulates strings with word parsing rules of UNIX Bourne shell | 
 | Singleton | lib | 
| Implementation of the Singleton pattern for Ruby | 
 | Socket | ext | 
| Access underlying OS socket implementations | 
 | StringIO | ext | 
| Pseudo I/O on String objects | 
 | StringScanner | ext | 
| Provides lexical scanning operations on a String | 
 | Sync | lib | 
| A module that provides a two-phase lock with a counter, see Sync_m | 
 | Syslog | ext | 
| Ruby interface for the POSIX system logging facility | 
 | Tempfile | lib | 
| A utility class for managing temporary files | 
 | Test::Unit | gem | 
| test-unit (Test::Unit) is unit testing framework for Ruby, based on xUnit principles. It allows writing tests, checking results and automated testing in Ruby. | 
 | ThreadsWait | lib | 
| Watches for termination of multiple threads | 
 | Time | lib | 
| Extends the Time class with methods for parsing and conversion | 
 | Timeout | lib | 
| Auto-terminate potentially long-running operations in Ruby | 
 | Dir | lib | 
| Extends the Dir class to manage the OS temporary file path | 
 | Tracer | lib | 
| Outputs a source level execution trace of a Ruby program | 
 | TSort | lib | 
| Topological sorting using Tarjan's algorithm | 
 |  | lib | 
| Utilities to replace common UNIX commands | 
 | UnicodeNormalize | lib | 
| Provides three String 'unicode_normalize' methods | 
 | URI | lib | 
| A Ruby module providing support for Uniform Resource Identifiers | 
 | WeakRef | lib | 
| Allows a referenced object to be garbage-collected | 
 | WEBrick | lib | 
| An HTTP server toolkit for Ruby | 
 |  | ext | 
| Win32 Registry, SSPI (Security Support Provider Interface) | 
 | WIN32OLE | ext | 
| Provides an interface for OLE Automation in Ruby | 
 | XMLRPC | gem | 
| XMLRPC is a lightweight protocol that enables remote procedure calls over HTTP. | 
 | YAML | lib | 
| Ruby client library for the Psych YAML implementation | 
 | YAML::DBM | lib | 
| YAML::DBM is a ::DBM type interface which allows YAML for values | 
 | YAML::Store | lib | 
| Store provides the same functionality as PStore, except it uses YAML to dump objects instead of Marshal. | 
 | Zlib | ext | 
| Ruby interface for the zlib compression/decompression library |