celluloid.rb

require 'celluloid'

class Cell
  include Celluloid

  def expensive
    puts "[Started]"
    sleep 1
    puts "[Finished]"
  end
end

cell = Cell.new
3.times.map do
  cell.async.expensive
end

sleep

=begin
Outputs:

[Started]
[Started]
[Started]
[Finished]
[Finished]
[Finished]
=end