Spigot
This is a javascript library that allows you to queue up as many jobs as you want and process them at a specified concurrency rate.
var Spigot = concurrency = 2 // process 2 jobs at a time (at most) var spigot = concurrency { console; ;}; spigot; spigot; spigot; for var i = 0; i < 100; ++i spigot;