How to: Core Extensions
* [ActiveSupport](https://github.com/rails/rails/tree/master/activesupport) - A collection of utility classes and standard library extensions.
* [Addressable](https://github.com/sporkmonger/addressable) - Addressable is a replacement for the URI implementation that is part of Ruby's standard library. It more closely conforms to RFC 3986, RFC 3987, and RFC 6570 (level 4), providing support for IRIs and URI templates.
* [Bitwise](https://github.com/kenn/bitwise) - Fast, memory efficient bitwise operations on large binary strings
* [Finishing Moves](https://github.com/forgecrafted/finishing_moves) - Small, focused, incredibly useful methods added to core Ruby classes. Includes the endlessly useful `nil_chain`.
* [Docile](https://github.com/ms-ati/docile) - A tiny library that lets you map a DSL (domain specific language) to your Ruby objects in a snap.
* [dry-rb](https://github.com/dry-rb) - dry-rb is a collection of next-generation Ruby libraries, each intended to encapsulate a common task.
* [Hamster](https://github.com/hamstergem/hamster) - Efficient, immutable, and thread-safe collection classes for Ruby.
* [Hanami::Utils](https://github.com/hanami/utils) - Lightweight, non-monkey-patch class utilities for Hanami and Ruby app.
* [MemoWise](https://github.com/panorama-ed/memo_wise) - Memoize any instance/class/module method, including support for frozen objects - rigorously tested and benchmarked on all Rubies - fast performance of memoized reads.
* [Ruby Facets](https://github.com/rubyworks/facets) - The premiere collection of general purpose method extensions and standard additions for Ruby.
* [Trick Bag](https://github.com/keithrbennett/trick_bag) - Assorted Ruby classes and methods to simplify and enhance your code.
* Attributes
  * [ActiveAttr](https://github.com/cgriego/active_attr) - What ActiveModel left out.
  * [Virtus](https://github.com/solnic/virtus) - Attributes on Steroids for Plain Old Ruby Objects.
  * [AttrExtras](https://github.com/barsoom/attr_extras) - Takes some boilerplate out of Ruby with methods like attr_initialize.
* Hash
  * [Hashie](https://github.com/intridea/hashie) - A collection of tools that extend Hashes and make them more useful.
* String
  * [string_pattern](https://github.com/MarioRuiz/string_pattern) - Generate strings supplying a simple pattern.