Ruby Document Database is a database that can store documents as the name suggests. The documents are stored in a key value pair format, which is very similar to how you would use a Hash. The document database has been used in many popular applications such as Facebook and Github. The reason why it is so popular is because of its simplicity to use queries and because it works best with JSON data.
mongify provides an ActiveRecord-like interface for working with MongoDB objects. It includes support for defining the schema for the models you are using, creating model instances and saving them back to the database. post_json provides a way to serialize a Ruby object into JSON and then save it to MongoDB as a BSON document. If you have an existing application that uses ActiveRecord or Mongoid and want to integrate with MongoDB without changing much in your code base, this library is good choice. serenity provides a simple way to create and delete documents in MongoDB via CRUD operations without having to worry about saving them through ActiveRecord or Mongoid classes. This library is useful if you want to use MongoDB as your data store without getting involved in the details of how it works. There are several popular open source Ruby Document Database libraries available for developers