What's the proper way to run Ruby scripts in parallel?

Current I have the following code to run some ruby scripts, within a ruby script:

def run(base_directory, run_count)
  working_directory = base_directory.gsub("\n","")
  for i in 1..run_count
    system("ruby " + working_directory + i.to_s + "\\" + "main.rb " +   working_directory + i.to_s + "\\")
  end
end

However this runs the scripts in a sequence, but I need them to run in parallel. Where I have 10 scripts to run, and I want to run 5 at a time until I reach the number of scripts that needs run. Is there a simple way to accomplish this?

via Chebli Mohamed