promise on array and streams. http://stackoverflow.com/q/22475917/157260

promise-parallel.js

var fs              = require('fs'),
    path            = require('path'),

    Promise         = require('rsvp').Promise,
    request         = require('request'),

    files           = [
        'https://www.google.com/images/srpr/logo11w.png',
        'http://rack.1.mshcdn.com/media/ZgkyMDEzLzA5LzE2L2JjL0Jpbmdsb2dvb3JhLmFkYjJkLnBuZwpwCXRodW1iCTEyMDB4OTYwMD4/996d9598/35b/Bing-logo-orange-RGB.png',
        'http://assets.fontsinuse.com/static/use-media-items/15/14246/full-2048x768/52c4c6bc/Yahoo_Logo.png'
    ];
    
var process = files.map(function (url) {
    return downloadFile(url).then(extractFile);
});

Promise.all(process)
    .then(function () {
        console.log('done processing');
    })
    .then(null, function () {
        console.log('error processing');
    });

promise-waterfall.js

var fs              = require('fs'),
    path            = require('path'),

    Promise         = require('rsvp').Promise,
    request         = require('request'),

    files           = [
        'https://www.google.com/images/srpr/logo11w.png',
        'http://rack.1.mshcdn.com/media/ZgkyMDEzLzA5LzE2L2JjL0Jpbmdsb2dvb3JhLmFkYjJkLnBuZwpwCXRodW1iCTEyMDB4OTYwMD4/996d9598/35b/Bing-logo-orange-RGB.png',
        'http://assets.fontsinuse.com/static/use-media-items/15/14246/full-2048x768/52c4c6bc/Yahoo_Logo.png'
    ];

// waterfall - process next file only after previous one is done
files.reduce(function (sequence, next) {
    return sequence.then(function () {
        return downloadFile(next).then(extractFile);
    });
}, Promise.resolve())
.then(function () {
    console.log('done processing files');
})
.then(null, function (err) {
    console.log('error processing files', err);
});

function downloadFile(url) {
    return new Promise(function (resolve, reject) {
        var destination = path.basename(url);
        request(url).pipe(fs.createWriteStream(destination))
            .on('close', function () {
                resolve(url);
            })
            .on('error', function (err) {
                reject(err);
            });
    });
}

function extractFile (url) {
   var file = path.basename(url);
   if (path.extname(file) !== '.zip') {
        return Promise.resolve(url); // NOOP
   }
   // extract file
   return Promise.reject(new Error('not implemented'));
}

rxjs-array-download.js

var fs              = require('fs'),
    path            = require('path'),

    request         = require('request'),
    Rx              = require('rx'),

    files           = [
        'https://www.google.com/images/srpr/logo11w.png',
        'http://rack.1.mshcdn.com/media/ZgkyMDEzLzA5LzE2L2JjL0Jpbmdsb2dvb3JhLmFkYjJkLnBuZwpwCXRodW1iCTEyMDB4OTYwMD4/996d9598/35b/Bing-logo-orange-RGB.png',
        'http://assets.fontsinuse.com/static/use-media-items/15/14246/full-2048x768/52c4c6bc/Yahoo_Logo.png'
    ];

Rx.Observable.fromArray(files)
    .selectMany(function downloadFile(url) {
        var subject         = new Rx.AsyncSubject(),
            destination     = path.basename(url);

        request(url).pipe(fs.createWriteStream(destination))
            .on('close', function () {
                subject.onNext(url);
                subject.onCompleted();
            })
            .on('error', function (err) {
                subject.onError(err);
            });

        return subject;
    })
    .filter(function (file) {
        return path.extname(file) === '.zip';
    })
    .selectMany(function unzip (file) {
        return Rx.Observable.throw(new Error('not implemented'));
    })
    .subscribe(function onNext () {
    }, function onError (err) {
        console.log(err);
    }, function onCompleted () {
        console.log('done');
    });