Following TDD practice, designed with few useful patterns, styled with rubocop style guide, documented with yard convention, lines of code analysis, 100% tests coverage and properly error handled rubygem project could be very useful to assess one's knowledge in build rubygems.

Yep

Undirected graph implementation for Mongoid

A client for MongoHQ API

Custom Ability class that allows CanCanCan authorization library store permissions in MongoDB via the Mongoid gem.

Minimal set of classes and modules to help with activity tracking.

Favoriting functionality for your Mongoid models

Add and manipulate flags (boolean values) on mongoid models

Generate frequency maps using mongodb aggregations

Undirected graph implementation for Mongoid

Mongoid field extension that serializes/deserializes IceCube Schedule and Rule objects.

Simple list behavior for Mongoid

A patch for mongoid localized fields, making it fallback through locale values that are not only `:nil?` but also `:blank?`.

Selectively validate presence in Monogid localized fields

Facilitates aggregations for events with multiple occurrences or a recurring schedule.

Makes one's life easier when working with events that have multiple occurrences, or a recurring schedule.

Mongoid field extension simplifying path parsing.

Custom field type for Mongoid that automatically converts strings to URL slugs.

Recurring date time fields for Mongoid models.

Toggleable attributes for your Mongoid models.