rufus-scheduler

Job scheduler for Ruby (at, cron, in and every jobs).
It uses threads.
Note: maybe are you looking for the README of rufus-scheduler 2.x? (especially if you're using Dashing which is stuck on rufus-scheduler 2.0.24)
Quickstart:
# quickstart.rb
require 'rufus-scheduler'
scheduler = Rufus::Scheduler.new
scheduler.in '3s' do
puts 'Hello... Rufus'
end
scheduler.join
#
# let the current thread join the scheduler thread
#
# (please note that this join should be removed when scheduling
# in a web application (Rails and friends) initializer)