Additional Resources
There are a number of good resources appearing all over the web for learning about MongoDB and Ruby. A useful selection is listed below. If you know of others, do let us know.
Screencasts
Introduction to MongoDB - Part I
An introduction to MongoDB via the MongoDB shell.
Introduction to MongoDB - Part II
In this screencast, Joon You teaches how to use the Ruby driver to build a simple Sinatra app.
Introduction to MongoDB - Part III
For the final screencast in the series, Joon You introduces MongoMapper and Rails.
RailsCasts: MongoDB & MongoMapper
Ryan Bates' RailsCast introducing MongoDB and MongoMapper.
Ryan Bates' RailsCast introducing Mongoid.
Presentations
Introduction to MongoDB (Video)
Mike Dirolf's introduction to MongoDB at Pivotal Labs, SF.
MongoDB: A Ruby Document Store that doesn't rhyme with 'Ouch' (Slides)
Wynn Netherland's introduction to MongoDB with some comparisons to CouchDB.
MongoDB (is) for Rubyists (Slides)
Kyle Banker's presentation on why MongoDB is for Rubyists (and all human-oriented programmers).
Articles
Why I Think Mongo is to Databases What Rails was to Frameworks
What if a key-value store mated with a relational database system?
John Nunemaker's articles on MongoDB and his Mongo Tips blog.
A series of articles on aggregation with MongoDB and Ruby:
Does the MongoDB Driver Support Feature X?
An explanation of how the MongoDB drivers usually automatically support new database features.
Projects
Sync your local development db with your remote production db using capistrano.
A very simple pub/sub system.
An extensible thread safe job/message queueing system that uses MongoDB as the persistent storage engine.
A port of the Github's Resque to MongoDB.
A Rails plugin for browsing and managing MongoDB data. See the live demo.
Resource Oriented Architecture (REST) for Sinatra and MongoMapper.
A simple social news application demonstrating MongoMapper and Rails.
From Sunlight Labs, a non-trivial application using MongoMapper and Sinatra.
An example application using Mustache, MongoDB, and Sinatra.
A question and answer site similar to Stack Overflow. Live version at shapado.com.
Libraries
An extension to ActiveRecord to allow the storage of arbitrary attributes in MongoDB.
ActsAsTree implementation for MongoMapper.
Machinist adapter (MongoMapper)
Machinist adapter using MongoMapper.
A delegation library for experimenting with production data without altering it. A quite useful pattern.
Remarkable Matchers (MongoMapper)
Testing / Matchers library using MongoMapper.
OpenIdAuthentication, supporting MongoDB as the datastore
Brandon Keepers' fork of OpenIdAuthentication supporting MongoDB.
MongoTree adds parent / child relationships to MongoRecord.
A plugin for the Merb framework for supporting MongoMapper models.
A web analytics tool.
A Rack middleware component that creates HTTP endpoints for files stored in GridFS.