Not only does it let you code complicated business logic easier, but it also helps you keep controllers well-readable and models loose-coupled to each other.

A lightweight, high-speed service layer for Rails applications

ServicePattern for Ruby on Rails.

Easily proxy paths in your rails application to other backend services.

Manage Ruby Service Objects.

Bare-boned service objects.

Handling SES notifications like Bounce or Complaint.

Store attributes in handy singletons for Rails/ActionDispatch sessions

Session Authentication

A gem for JS clients to check if their session has expired.

SessionGem for knowledge sessions.

session_jsonizer is a simple library for Rails 3 and 4 to serialize session as JSON in the same format.

A simple rails engine that makes logging and testing easier

A session Active Model.

Quick concern for session variables

Supports Rails session store relocation with duplicate write session data to multiple stores

A gem for describing constraints on data sets

SetThingsEngineTest

System for managing global settings trough database

Keep application settings in the database