Hi All, The best gem or plugin for rails application as below, 1. Geo location or google map - https://github.com/alexreisner/geocoder 2. Rails Authentication - https://github.com/plataformatec/devise 3. Twitter API - https://github.com/sferik/twitter 4. File Uploads - https://github.com/thoughtbot/paperclip 5. Deployment Automation - https://github.com/capistrano/capistrano 6. E-Commerce - https://github.com/spree/spree 7. Rails Admin Interfaces - https://github.com/gregbell/active_admin 8. Rails Pagination - https://github.com/mislav/will_paginate 9. Rails Search - https://github.com/sunspot/sunspot 10. Rails Ratings/votings - https://github.com/edgarjs/ajaxful-rating 11. Web servers - https://github.com/macournoyer/thin 12. Exception Notification - https://github.com/rails/exception_notification 13. JavaScript Frameworks - https://github.com/jquery/jquery 14. Rails Captcha - https://github.com/ambethia/recaptcha 15. Rails Comments - https://github.com/jackdempsey/acts_as_commentable 16. Scheduling tasks - https://github.com/javan/whenever 17. facebook API - https://github.com/mmangino/facebooker 18. Sitemap generator - https://github.com/kjvarga/sitemap_generator 19. JavaScript and CSS Asset Compression for Production Rails Apps - https://github.com/sbecker/asset_packager 20. Rails Permalinks & Slugs - https://github.com/norman/friendly_id 21. E-Mail Sending - https://github.com/mikel/mail 22. Markup processors (html convert) - https://github.com/rtomayko/rdiscount/ 23. Rails Captcha - https://github.com/ambethia/recaptcha 24. PDF Generation - https://github.com/sandal/prawn 25. Ruby Version Management - https://github.com/wayneeseguin/rvm 26. Background Jobs - https://github.com/collectiveidea/delayed_job Useful Links 1. Ruby regular expression editor - http://rubular.com/ 2. Convert Html Snippets to Haml Snippets - http://html2haml.heroku.com/ 3. Convert CSS Snippets to Syntactically Awesome StyleSheets code - http://css2sass.heroku.com/ 4. displaying images, html content and multi-media in a Mac-style "lightbox" that floats overtop of web page - http://fancybox.net/ 5. The online event registration and ticketing tool - https://www.amiando.com/ 6. Epoch & Unix Timestamp Conversion - http://www.epochconverter.com/ 7. Email Delivery - http://sendgrid.com/ 8. Online image converter - http://www.go2convert.com/ 9. Web Page Validation - http://www.w3schools.com/site/site_validate.asp 10. Web technology information profiler tool - http://builtwith.com/