d8-phing uses composer to install requirements - http://getcomposer.org/
To install Composer, you just need to download the composer.phar executable.
curl -sS https://getcomposer.org/installer | php
Then run:
php composer.phar
d8-phing uses the DrushTask class to run Drush commands via Phing. The DrushTask class is maintained in the phingdrushtask project on Drupal.org and was created by mongolito404.