Below is a (non-exhaustive) list of curated Rails Gems we use at ClearCove in 2019:

• active_interaction - Manage application specific business logic.
• acts_as_list - ActiveRecord plugin for managing lists.
• ahoy_matey - Analytics for Rails, in combination with Blazer.
• bootstrap-rubygem - Bootstrap 4 rubygem for Rails.
• clearance - Rails authentication with email & password.
• closure_tree - Easily and efficiently make your ActiveRecord models support hierarchies.
• cocoon - Dynamic nested forms using jQuery made easy.
• dotenv-rails - Load environment variables from .env.
• filterrific - Filter, search, and sort your ActiveRecord lists.
• haml - HTML Abstraction Markup Language.
• pg - Ruby interface to PostgreSQL.
• puma - A Ruby web server built for concurrency.
• pundit - Rails authorization library.
• rubocop - Ruby static code analyzer and formatter.
• sass-rails - Stylesheet engine for Sass.
• sidekiq-scheduler - Lightweight job scheduler extension for Sidekiq.
• sidekiq - Simple, efficient background processing for Ruby
• state_machines-activerecord - StateMachines Active Record Integration
• will_paginate - For ActiveRecord pagination.

Ruby Toolbox is a great resource to find awesome gems for your Rails app.