I don't know about "can't survive" part but here's a long list of gems I use or like and find useful: Utils: devise, omniauth, cancan, squeel, ransack, active_

I don't know about "can't survive" part but here's a long list of gems I use or like and find useful: Utils: devise, omniauth, cancan, squeel, ransack, active_scaffold, rails_config, switch_user, simple_form, navigasmic, sentient_model, userstamp, mail_form, carrierwave, state_machine, concerned_with, kaminari, recommendable, jbuilder, ancestry, acts_as_nested_set, acts_as_nested_interval [ my gem :) ], paper_trail, version_fu, pdfkit, wicked_pdf, wkhtmltopdf-binary, delayed_job, whenever, active-model-email-validator, nested_form, cocoon, bitfields Test: rspec-rails, factory_girl_rails, faker, capybara, shoulda, database_cleaner, simplecov, spork, guard, capybara-webkit, timecop, vcr, fakeweb, capybara-mechanize, capybara-selenium-remote Assets: compass-rails, sass-rails, bootstrap-sass, jquery-rest-rails, fullcalendar-rails, underscore-rails, jquery-ui-rails, coffee-rails, chosen-rails, pjax_rails, rails-backbone, jquery-rails Development: mongrel, debugger, mailcatcher Production: dalli, exception_notification, capistrano, capistrano-ext