This is yet another RSS / Atom feed generator for PHP 5.5 and later. It works great in combination with Flow but should also be fine as a standalone library.
This package is composer enabled.
<?php
$feed = new Feed();
$channel = new Channel();
$channel
->setTitle('All about TYPO3 Flow')
->setDescription($channelDescription)
->setFeedUri($feedUri)
->setWebsiteUri($websiteUri)
->setLanguage('en-US');
$item = new Item();
$item
->setTitle('My first blog post')
->setGuid($someUniqueIdentifier)
->setPublicationDate(new \DateTime())
->setContent($blogPostContent);
$channel->addItem($item);
$feed->addChannel($channel);
echo $feed;