FeedsActiveRecord Default Values
default_value_for and active_record_defaults
ActiveRecord Encryption
attr_encrypted, strongbox, sentry, Lockbox, lucifer, and more
ActiveRecord Index Assist 
rails_indexes and ambitious_query_indexer
ActiveRecord Named Scopes
searchlogic, pacecar, utility_scopes, can_search, and more
ActiveRecord Nesting
awesome_nested_set, ancestry, acts_as_tree, and more
ActiveRecord Soft Delete
acts_as_paranoid, acts_as_archive, and more
ActiveRecord Sortables
acts_as_list and sortable
ActiveRecord Value Cleanup
attribute_normalizer, strip_attributes, nilify_blanks, and more
ActiveRecord Versioning
acts_as_versioned, vestal_versions, paper_trail, and more
API Clients
twitter, googlecharts, garb, aws-s3, amazon-ec2, and more
Backups
safe, backup_fu, backup, and db2s3
Browser testing
webrat, capybara, culerity, watir, celerity, and more
Calendars
calendar_helper, event_calendar, later_dude, and more
Code Metrics
metric_fu, rcov, reek, roodi, report_card, and rcov_plugin
Content Management
radiant, browsercms, adva_cms, typo, refinerycms, and nesta
Continuous Integration
cruisecontrol.rb, cijoe, integrity, signal, cap_gun, and more
Continuous Testing
watchr and zentest
CouchDB Clients
couch_potato, couch_foo, couchrest, relaxdb, and more
CSS Frameworks
blueprint-css, compass, oocss, fluid960gs, elastic, and more
CSS with Ruby
less, deadweight, css_dryer, and sass
Daemon Management
daemon_controller and daemon-spawn
Daemonizing
daemon-kit, robustthread, daemon_generator, daemons, and more
Dependency Management
bundler, braid, piston, cached_externals, giternal, and more
Deployment Automation
moonshine, rubber, inploy, capistrano, vlad, and more
Documentation Tools
yard, hanna, sdoc, ajax-rdoc, erbook, and ron
E-Commerce
spree, active_merchant, invoicing, shippinglogic, and more
mail, pony, tmail, mail_queue, resque_mailer, and popthis
Exception Notification
exception_notification, hoptoad_notifier, and more
Game libraries
rubygame, gosu, gamebox, chingu, and jemini
Gem Creation
jeweler, newgem, bones, echoe, hoe, and simple-gem
Gem Doc Viewers
bdoc, gembox, sinatra-rubygems, and docbox
Geocoding & Maps
geokit-gem, geokit-rails, graticule, acts_as_geocodable, and more
Graphing
open_flash_chart, gruff, rifgraf, seer, and more
HTML parsing
nokogiri, hpricot, scrubyt, scrapi, and libxml-ruby
HTTP clients
httparty, rest-client, mechanize, typhoeus, patron, and more
I18n
globalize2, translate_routes, i18n, fast_gettext, and more
Image Processing
mini_magick, image_science, devil, and im_magick
irb Tools
dotfiles, hirb, looksee, utility-belt, sketches, and bond
IRC Bots
autumn, isaac, rbot, summer, and sprinkles
JavaScript Frameworks
scriptaculous, jquery, prototype, mootools-core, yui3, and more
JavaScript Testing
blue-ridge, jspec, testswarm, screw-unit, and more
JavaScript Tools
sprockets, juicer, jabs, frontcompiler, packr, and jake
LDAP
authlogic_ldap, ruby-net-ldap, and more
Markup processors
rdiscount, redcloth, bluecloth, rpeg-markdown, and maruku
Microformats
mofo, prism, microformats_helper, and assert-microformats
Mocking
rr, mocha, stump, flexmock, and facon
Mocking Web Requests
fakeweb, webmock, and netrecorder
Music & MIDI
archaeopteryx, midiator, jazztoolbox, and more
Packaging Systems
rip, coral, spoke, and ruby-which
Packaging to Executables
crate, ocra, and rubyscript2exe
PDF Generation
prawn, prawnto, princely, wkhtmltopdf, kitabu, and rghost
Project Management
redmine, retrospectiva, Teambox-2, and oupsnow
Prototype Replacements
jrails, jquery-ui-rails-helpers, and yui_on_rails
Queueing
delayed_job, resque, workling, amqp, cloud-crowd, and more
Rails Admin Interfaces
active_scaffold, typus, admin_data, streamlined, and more
Rails App Templates
rails-templates, BigOldRailsTemplate, rails-template, and more
Rails Asset Management
asset_packager, jammit, smurf, bundle-fu, rucksack, and more
Rails Authentication
authlogic, restful-authentication, devise, clearance, and more
Rails Authorization
declarative_authorization, cancan, acl9, and more
Rails Captcha
recaptcha, negative-captcha, brain_buster, captcha, and more
Rails Comments
acts_as_commentable, disqus, and more
Rails Controller Abstractions
inherited_resources, resource_controller, and more
Rails DB Bootstrapping
seed-fu, populator, bootstrapper, and db-populate
Rails File Uploads
paperclip, attachment_fu, carrierwave, imagery, and more
Rails Fixture Replacement
factory_girl, machinist, object_daddy, dataset, fixjour, and more
Rails Form Builders
formtastic, semantic_form_builder, and more
Rails In-Place Editing
in_place_editing, rest_in_place, and more
Rails Instrumentation
rails-footnotes, rpm, rails_metrics, rackamole, and more
Rails Menu Builders
semantic-menu, simple-navigation, simple_navigation, and more
Rails Pagination
will_paginate, paged_scopes, sort_by, and has_paginate
Rails Permalinks & Slugs
friendly_id, permalink_fu, stringex, find_by_param, and more
Rails Ratings
ajaxful-rating, acts_as_rateable, is_rateable, and more
Rails Search
thinking-sphinx, sunspot, acts_as_ferret, ferret, and more
Rails Subdomains
subdomain-fu, subdomain_routes, subdomain_account, and more
Rails Tagging
acts-as-taggable-on, is_taggable, and more
Rails Wizards
wizardly, actsaswizard, wizard, and partially_valid
Random Data Generation
forgery, randexp, faker, and random_data
Recurring Events
recurrence, runt, schedule_fu, recurring_event, and more
RSS Feed Parsing
feedzirra, feed-normalizer, feed_me, simple-rss, and more
Scheduling
whenever, rufus-scheduler, craken, and Taskit
Scripting Frameworks
thor, rake, boson, and sake
Security Tools
rails_xss, tarantula, loofah, xss_terminate, and more
Server Monitoring
visage and webstats
SOAP Clients
savon, handsoap, and serviceproxy
Social Network Builders
insoshi, communityengine, lovd-by-less, acts_as_network, and more
Spam Detection
rakismet, viking, defender, defensio-ruby, akismetor, and more
State Machines
aasm, state_machine, ruote, workflow, state-fu, and more
Static Website Generation
jekyll, webby, toto, staticmatic, korma, and bonsai
Syntax Highlighting
highlight, harsh, tm_syntax_highlighting, and more
Systems Integration
chef, sprinkle, passenger-stack, puppet, vagrant, and rudy
Template Languages
haml, liquid, mustache, erector, parkaby, and ruhl
Testing frameworks
cucumber, rspec, shoulda, riot, bacon, and matchy
Text Editors in Ruby
redcar, diakonos, and arcadia
Time Warping
delorean, time-warp, and time-zone-warp
Visualizing Data
raphael and ruby-processing
Web app frameworks
rails, sinatra, merb-core, ramaze, cramp, and rackable
Web servers
passenger, thin, unicorn, mongrel, and ebb
Wiki Apps
git-wiki, instiki, signal-wiki, collective, perwikity, and more
XML Mapping
happymapper, sax-machine, roxml, and representative