node.js async libs

I use Async.js.

Async is a utility module which
provides straight-forward, powerful
functions for working with
asynchronous JavaScript. Although
originally designed for use with
node.js, it can also be used directly
in the browser.

Examples

async.map(['file1','file2','file3'], fs.stat, function(err, results){
    // results is now an array of stats for each file
});

async.filter(['file1','file2','file3'], path.exists, function(results){
    // results now equals an array of the existing files
});

async.parallel([
    function(){ ... },
    function(){ ... }
], callback);

async.series([
    function(){ ... },
    function(){ ... }
]);