collect_subclasses.rb

class BusinessEvent
  def self.subclasses
    subclasses = []
    ObjectSpace.each_object(Module) {|m| subclasses << m if m.ancestors.include? self and m != self}
    subclasses
  end
end

class OrderEvent < BusinessEvent
end

class PurchaseEvent < BusinessEvent
end

class CustomerEvent < BusinessEvent
end

puts BusinessEvent.subclasses.inspect
# => [CustomerEvent, PurchaseEvent, OrderEvent]