gistfile1.js

var async = require('async');

function one(cb) {
    console.log("running one");
    cb(null, function () { return "one" });
}

function two(cb) {
    console.log("running two");
    function three(callback){
        console.log("running three");
        var a = [];
        for (var i = 1; i <= 3; i++) {
            a.push(i);
        };
        callback(null, function () { return "three"}, a);
    }

    function four(last, a, callback) {
        console.log("running four");
        console.log(a);
        callback(null, [last, function () { return "four"}]);
    }

    async.waterfall([three, four], cb);
}

function five(cb) {
    console.log("running five");
    cb(null, function () { return "five" });
}

function output(error, results) {
    // if (error) ...
    var flat = [];
    results.forEach(function (r) {
      flat = flat.concat(r);
    });
    flat.forEach(function (fn) {
      console.log(fn());
    });
}

async.series([one, two, five], output);