jQuery Deferred Queue:

Easily execute sets of asynchronous JavaScript code. The queue can be paused and resume on demand.

This especially useful when chaining together groups of animations that may vary in duration.

Example:

var animator = $.DeferredQueue();

function move_to(elem, position){
	// return a function that gets called when set is executed
	return function(){
		// function returns a promise
		return elem.animate(pos, Math.random() * 5000);
	}
}

// each set gets called with $.when when it is dequeued
animator.queue(
	move_to(one, { top: 250, left: 250 }),
	move_to(two, { top: 250, left: 50 }),
).queue(
	move_to(one, { top: 50, left: 50 }),
	move_to(two, { top: 50, left: 250 }),
).queue(
	move_to(one, { top: 250, left: 250 }),
	move_to(two, { top: 250, left: 50 }),
).queue(
	move_to(one, { top: 50, left: 50 }),
	move_to(two, { top: 50, left: 250 }),
);