Addressable is a replacement for the URI implementation that is part of Ruby's standard library. It more closely conforms to the relevant RFCs and adds support for IRIs and URI templates.
Just some algorithm implementations
A Relational Algebra
CLI Steps for Cucumber
Adds the ability to normalize and format attributes cleanly with code blocks
Showoff presentation on building gems
A rails plugin/gem to kill N+1 queries and unused eager loading
Manage your application's gem dependencies with less pain
Demonstration of a bug in bundler
webrat alternative which aims to support all browser simulators
A Rails plugin/gem that provides an API to declare which string columns in your models should be case (in)sensitive.
Ruby interface to the Clickatell SMS Gateway API
Keeps track of when a specific column in an ActiveRecord model changed.
Crowd-sourced Ruby conference wiki
Campfire notifiier for CruiseControl.rb.
Just some practice coding problems for an upcoming interview
BDD that talks to domain experts first and code second
Generate difference sets between Ruby sequences.
My .vim files
config files for zsh, bash, completions, gem, git, irb, rails
Blacklist particular email addresses so ActionMailer doesn't deliver emails to them.
Define equality, equivalency and hash methods automatically
Erlang IDNA lib
EXtended http(s) CONnections
Preload data created by factory girl (or any other Rails fixtures alternative) so that you can use Rails' built-in test transactions.
A tool for faking responses to web requests, originally by Blaine Cook
Simple, but flexible HTTP client library, with support for multiple backends.
MiniTest/RSpec/Cucumber formatter that gives each test file its own line of dots
Code for the old fractalcomposer.com