Arel is a Relational Algebra for Ruby. It 1) simplifies the generation complex of SQL queries and it 2) adapts to various RDBMS systems. It is intended to be a framework framework; that is, you can build your own ORM with it, focusing on innovative object and collection modeling as opposed to database compatibility and query generation.

Adds the missing outer_joins method to ActiveRecord

Restrict the values assignable to ActiveRecord attributes or associations

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).

https://github.com/tsukasaoishi/fresh_connection

Rails style structure for GraphQL API.

Double entry bookkeeping with Rails

A user-centric voting extension for Rails 3 applications.

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

Let ActiveRecord serialize and cast your UUIDs to and from binary columns in your database.

Provides automatic deadlock retry and logging functionality for ActiveRecord and MySQL

Paperclip-Azure is a [Paperclip](https://github.com/thoughtbot/paperclip) storage driver for storing files in a Microsoft Azure Blob.

An extension to paper_trail, using this you can fetch actual object who was responsible for this change

Organize ActiveRecord model into a tree structure using PostgreSQL LTree

Easily write arbitrary filters

Build complex SQL queries by defining each subquery separately. Query::Composer will then compose those subqueries together, nesting as needed, to produce the final SQL query.

Properties gem for Ruby on Rails

Positionless model sorting for Rails.

Real stubs and spies for HTTP(S) services

Adds shorthands and conveniences to ActiveRecord's handling of indexes