Mongoose is a project mainly written in Ruby, it's free.
This is a sandbox application that uses Rails 3.0.10, Devise 1.4.5, and Mongoid 2.2.3 as the OM layer.
It could be used as a template application for other Mongo applications that need authentication.
All code is AS-IS.
You'll need to install the gems and also make sure you have access to a MongoDb. By default this is set to localhost for development and production.
Sign up using http://localhost:3000/members/sign_up
This stores the member details in MongoDb