The JitPreloader has the ability to send notifications when N+1 queries occur to help guage how problematic they are for your code base and a way to remove all of the commons explicitly or automatically

Connection proxy for ActiveRecord for single master / multiple slave database deployments

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

An awesome nested set implementation for Active Record

Write-through and Read-through Cacheing for ActiveRecord

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)

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.

A Postgres advisory lock client

Helps to save your eyes, when reading hardcore SQL requests in console

Adds the ability to pull random records from ActiveRecord

A modern fast tagging framework for Rails 3.1+

Database-backed Action Cable backend.

State machine that allows dynamic transitions for business workflows

Sharding

Introspects your database string field maximum lengths and automatically defines length validations.

Backported from Rails 5.0 to use with 4.x versions

Any_of allows to compute dynamic OR queries.