The most gem that you need for developing Ruby on Rails project

1. haml-rails
Description: Haml-rails provides Haml generators for rails 3.
Source: https://github.com/indirect/haml-rails

2. bootstrap-sass
Description: bootstrap-sass is an sass-powered version of Twitter’s Bootstrap.
Source: https://github.com/thomas-mcdonald/bootstrap-sass

3. simple_form
Description: simple_form aims to be as flexible as possible while helping you with powerful components to create your form.
Source: https://github.com/plataformatec/simple_form

4. bootstrap Wysihtml5 for Rails
Description: It provides a stylish wysiwyg editor for Bootstrap.
Source: https://github.com/Nerian/bootstrap-wysihtml5-rails, http://jquery-spellchecker.badsyntax.co/bootstrap-wysihtml5.html

5. select2
Description: jQuery based replacement of select boxes. It supports searching, remote data sets, and infinite scrolling of results.
Source: https://github.com/argerim/select2-rails, http://ivaynberg.github.io/select2

6. nested_form
Description: This is a Rails gem for conveniently manage multiple nested models in a single form. It does so in an unobtrusive way through jQuery or Prototype.
Source: https://github.com/ryanb/nested_form

7. httparty
Description: makes http fun again.
Source: https://github.com/jnunemaker/httparty

8. typhoeus
Description: typhoeus runs HTTP requests in parallel while cleanly encapsulating handling logic.
Source: https://github.com/typhoeus/typhoeus

9. devise
Description: devise is a flexible authentication solution for Rails.
Source: https://github.com/plataformatec/devise

10. CanCan
Description: CanCan is an authorization library for Ruby on Rails.
Source: https://github.com/ryanb/cancan

11. rspec-rails
Description: rspec-rails is a testing framework for Rails 3.x and 4.x.
Source: https://github.com/rspec/rspec-rails

12. shoulda-matchers
Description: shoulda-matchers provides Test::Unit- and RSpec-compatible one-liners that test common Rails functionality.
Source: https://github.com/thoughtbot/shoulda-matchers

13. Capybara
Description: Capybara helps you test web applications by simulating how a real user would interact with your app.
Source: https://github.com/rspec/rspec-rails

14. factory_girl_rails
Description: factory_girl - A library for setting up Ruby objects as a test data.
Source: https://github.com/thoughtbot/factory_girl_rails

15. exception_notification
Description: exception_notification provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application.
Source: https://github.com/smartinez87/exception_notification

16. Pry
Description: Pry is a powerful alternative to the standard IRB shell for Ruby.
Source: https://github.com/pry/pry

17. browsernizer
Description: want friendly “please upgrade your browser” page? This gem is for you.
Source: https://github.com/assembler/browsernizer

18. zero-clipboard-rails
Description: add the zeroclipboard to your rails app.
Source: https://github.com/HaNdTriX/zeroclipboard-rails

19. uuidtools
Description: uuidtools was designed to be a simple library for generating any of the various types of uuids.
Source: https://github.com/sporkmonger/uuidtools/tree

20. will_paginate
Description: will_paginate is a pagination library that intergrates with Ruby on Rails.
Source: https://github.com/mislav/will_paginate

21. paperclip
Description: Paperclip is intended as an easy file attachment library for Active Record.
Source: https://github.com/thoughtbot/paperclip

22. delayed_job_active_record
Description: delayed_job_active_record encapsulates the common pattern of asynchronously executing longer tasks in the background.
Source: https://github.com/collectiveidea/delayed_job

23. pg_search
Description: pg_search builds named scopes that take advantage of PostgreSQL’s full text search.
Source: https://github.com/Casecommons/pg_search

24. activerecord-postgres-hstore
Description: activerecord-postgres-hstore - Goodbye serialize, hello hstore. Speed up hashes in the database.
Source: https://github.com/engageis/activerecord-postgres-hstore

25. fastimage
Description: fastimage finds the size or type of an image given its uri by fetching as little as needed.
Source: https://github.com/sdsykes/fastimage

26. better_error
Description: better errors replaces the standard Rails error page with a much better and more useful error page.
Source: https://github.com/charliesome/better_errors

27. vcr
Description: record your test suite’s HTTP interactions and reply them during future test runs for fast, deterministic, accurate tests.
Source: https://github.com/vcr/vcr

28. aws-sdk
Description: The official AWS SDK for Ruby.
Source: https://github.com/aws/aws-sdk-ruby

29. guard
Description: Guard is a command line tool to easily handle events on file system modifications.
Source: https://github.com/guard/guard

30. Spork
Description: Spork is Tim Harper’s implementation of test server.
Source: https://github.com/sporkrb/spork

31. strip_attributes
Description: StripAttributes is an ActiveModel extension that automatically strips all attributes of leading and trailing whitespace before validation. If the attribute is blank, it strips the value to nil by default.
Source: https://github.com/rmm5t/strip_attributes

32. exception_notification
Description: The Exception Notifier plugin provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application.
Source: https://github.com/rails/exception_notification

33. assets_helper
Description: is the gem that use to include css and javascript by controller name automatically, it mean that include only css and javascript file in the controller that you are running.
Source: https://github.com/Bunlong/assets_helper

34. activenavbar
Description: is the gem that use to set the active navbar link, a link becomes active when you click on it.
Source: https://github.com/Bunlong/activenavbar

35. olive
Description: is the rails helper gem that enables to use content_for in controllers.
Source: https://github.com/Bunlong/olive

36. Slim
Description: Slim is a template language whose goal is to reduce the view syntax to the essential parts without becoming cryptic.
Source: https://github.com/slim-template/slim

37. font-awesome-rails
Description: font-awesome-rails provides the Font-Awesome web fonts and stylesheets as a Rails engine for use with the asset pipeline.
Source: https://github.com/bokmann/font-awesome-rails

38. minimagick
Description: Using MiniMagick the ruby processes memory remains small (it spawns ImageMagick’s command line program mogrify which takes up some memory as well, but is much smaller compared to RMagick).
Source: https://github.com/minimagick/minimagick

39. byebug
Description: It allows you to see what is going on inside a Ruby program while it executes and offers many of the traditional debugging features.
Source: https://github.com/deivid-rodriguez/byebug

40. awesome_print
Description: Pretty print your Ruby objects with style – in full color and with proper indentation.
Source: https://github.com/michaeldv/awesome_print

41. omniauth
Description: OmniAuth is a library that standardizes multi-provider authentication for web applications. It was created to be powerful, flexible, and do as little as possible.
Source: https://github.com/intridea/omniauth

42. rails_layout
Description: Generates Rails application layout files for various front-end frameworks.
Source: https://github.com/RailsApps/rails_layout

43. bullet
Description: help to kill N+1 queries and unused eager loading.
Source: https://github.com/flyerhzm/bullet

44. pundit
Description: Minimal authorization through OO design and pure Ruby classes.
Source: https://github.com/elabs/pundit

45. devise_invitable
Description: An invitation strategy for devise.
Source: https://github.com/scambra/devise_invitable

46. draper
Description: Decorators/View-Models for Rails Applications.
Source: https://github.com/drapergem/draper