Give your models as-of date temporal extensions. Built entirely for PostgreSQL >= 9.4

Delayed is a multi-threaded, SQL-driven ActiveJob backend used at Betterment to process millions of background jobs per day. It supports postgres, mysql, and sqlite, and is designed to be Reliable (with co-transactional job enqueues and guaranteed, at-least-once execution), Scalable (with an optimized pickup query and concurrent job execution), Resilient (with built-in retry mechanisms, exponential backoff, and failed job preservation), and Maintainable (with robust instrumentation, continuous monitoring, and priority-based alerting).

Fast batch deletes for Active Record and Postgres

Ferry is a data migration and visualization command line tool rubygem that seeks to simplify the increasingly prevalent big data problems for developers

hydra_attribute is an implementation of EAV pattern for ActiveRecord models.

I18n date/number parsing/localization

Rails I18n library for ActiveRecord model/data translation using PostgreSQL's JSONB datatype. Translations are stored directly in the model table rather than shadow tables.

Organizes ActiveRecord models into a tree/hierarchy using a materialized path implementation based around PostgreSQL's ltree datatype. ltree's operators ensure that queries are fast and easily understood.

Ruby gem that automatically adds a lock timeout to all Active Record migrations

never let an unscoped Model.all accidentally leak data to an unintended audience.

Extend Ruby on Rails ActiveRecord with Neo4j nodes. Keep RDBMS and utilize the power of Neo4j queries. Originally by @elado.

An awesome nested set implementation for Active Record

Write-through and Read-through Cacheing for ActiveRecord

Disables observers during testing, allowing you to write model tests that are completely decoupled from the observer.

Create and modify your notifications through a simple API.

Integrates with your authentication solution to craft a personalized user notification platform.

A ruby library for working with the Open Archive Initiative Protocol for Metadata Harvesting (OAI-PMH)

use pagy for cursor-based pagination with rails

Extends Paperclip with Dropbox storage.

If you like the straight forward and effective nature of Strong Parameters and suspect that CanCan might be overkill for your project then you'll love Petergate's easy to use and read action and content based authorizations.