5. CommandCommand provides a simple object-oriented interface for running shell commands from Ruby.
7. MergerA gem for merging Active Record models
9. Random findersA Rails plugin that allows quick and easy fetching of random records, or records in random order.
11. With actionA respond_to style helper for doing different actions based on which request parameters are passed.
14. GraticuleGraticule is a geocoding API for looking up address coordinates and performing distance calculations, supporting many popular APIs.
15. AuditedAudited (formerly acts_as_audited) is an ORM extension that logs all changes to your Rails models.
16. InteractorInteractor provides a common interface for performing complex user interactions.
18. TinderTinder is a Ruby API for interfacing with Campfire, the 37Signals chat application.
21. delayed jobDatabase based asynchronous priority queue system -- Extracted from Shopify