Techniques to overcome the single inheritance issue?

what techniques are there in ruby to overcome the single inheritance rule?

is it just using modules?

Yes, modules are the answer in general. If you have a more specific needs (such as having a class that merges functionality from two different classes) other options exist, such as delegation.

Note that if you need a module to provide 'class' methods to those that inherit from it, you will probably want to use this common pattern:

module Foo
  def aaa
    "hi"
  end
  module ClassMethods
    def bbb
      "mom"
    end
  end
  def self.included( other )
    other.extend ClassMethods
  end
end

class Bar
  include Foo
end

puts Bar.new.aaa, Bar.bbb
#=> hi
#=> mom