A list of recommended gems :
- rails_12factor: follow the 12 factors methodology (http://12factor.net) - https://github.com/heroku/rails_12factor
- phony_rails: if you have to handle phone number seriously - https://github.com/joost/phony_rails
- launchy: if you have to emulate email/text sending (like letter_opener does) - https://github.com/copiousfreetime/launchy
- annotate: add your schema in your models - https://github.com/ctran/annotate_models
- active_record-acts_as: for multi-tables inheritance - https://github.com/hzamani/active_record-acts_as
- sitemap_generator: for SEO guru - https://github.com/kjvarga/sitemap_generator
- activerecord-typedstore: if you want to use the typedstore feature of PostgreSQL - https://github.com/byroot/activerecord-typedstore
- paranoia: when deletion is not really what you expect - https://github.com/rubysherpas/paranoia
- sanitize_email: don't mail your users in the sandbox/staging environment - https://github.com/pboling/sanitize_email
- httparty: another rest client, but do the job - https://github.com/jnunemaker/httparty
- devise: user authentication - https://github.com/plataformatec/devise
- friendly_id: slugify your objet (SEO friendly) - https://github.com/norman/friendly_id
- geocoder: get coordinates from various providers (don't forget to enable the cache) - https://github.com/alexreisner/geocoder
- money-rails: business is business, handle all currencies easily - https://github.com/RubyMoney/money-rails
- google_currency: for free exchange rate service - https://github.com/RubyMoney/google_currency
- paperclip: simple upload and images manipulation (rmagick companion) - https://github.com/thoughtbot/paperclip
- kaminari: paginate your objects - https://github.com/amatsuda/kaminari
- pretender: impersonate your users - https://github.com/pretenderjs/pretender
- rack-attack: rate limiting at the application level (perfect for Heroku) - https://github.com/kickstarter/rack-attack
- rubocop: static code analyzer - https://github.com/bbatsov/rubocop
- bullet: help to eager load data - https://github.com/flyerhzm/bullet
- rack-mini-profiler: optimizing tool - https://github.com/MiniProfiler/rack-mini-profiler
- hashids: hashed ids for your objects (invoices, users, ...)
- sift: official gem of siftsience, a fraud detection SaaS - https://github.com/SiftScience/sift-ruby