I was messing around with a project this week in Ruby, and right as I was trying to figure out how to best implement extensibility and modularity, this article came along.

Main module require'd from main.rb:

class Statement
  @@statementtypes = Array.new

  #implements plug-in nature of statements
  def self.inherited(stmttype)
    @@statementtypes << stmttype
  end
end

Dir["statements/*.rb"].each do |x|
  load x
end

And each .rb file in statements/ has a class that inherits from Statement.

No details yet on what the project is, aside from that it's fun and challenging.