I have a quick and dirty script running allready . Will post it later. It just loads the index.xml files in the forums and sorts them according to pubDate. Nothing fancy but it does what i need.

Thanks

With the help from Stackoverflow and Google :)
Quick and dirty small script that grabs the entrys and sorts them per date. The interesting part is between //====.
Defining feeds this way suits me well. You prabably need to do something recursive. The last part i just use to test and display.
This works fine for me right now but probably not for others.

%PHP
<?
//Define feeds
foreach (glob("*/index.xml") as $filename) {
$feeds[] = $filename;
}
//================================
// Get all feed entries
$entries = array();
foreach ($feeds as $feed) {
$xml = simplexml_load_file($feed);
$entries = array_merge($entries, $xml->xpath('/rss//item'));
}

// Sort feed entries by pubDate (descending)
usort($entries, function ($x, $y) {
return strtotime($y->pubDate) - strtotime($x->pubDate);
});

//================================
foreach ($entries as $entry){

echo "$entry->author." : ".$entry->title."<p>".$entry->pubDate."</p><p>".strip_tags(mb_substr($entry->description, 0, 100, 'UTF-8')) . '...';
?> 
%

Yes. This only scans subfora and only one level down. It you have nested fora, probably a good idea with many fora, then you probably need to use http://php.net/manual/en/class.recursivedirectoryiterator.php.
For me the above is very simple and works wonderful in my setup.

I've cleaned the code a bit this morning and put it in a function.

%
<?
function latestFeed($n) {
	$latest[]=NULL;
	foreach (glob("forum/*/index.xml") as $filename) {
		$feeds[] = $filename;
		}
// Get all feed entries
	$entries = array();
	foreach ($feeds as $feed) {
    	$xml = simplexml_load_file($feed);
    	$entries = array_merge($entries, $xml->xpath('/rss//item'));
	}

// Sort feed entries by pubDate (descending)
	usort($entries, function ($x, $y) {
    	return strtotime($y->pubDate) - strtotime($x->pubDate);
	});

	foreach (array_slice($entries,0,$n) as $entry){
		$entry->description=strip_tags(mb_substr($entry->description, 0, 100, 'UTF-8')) . '...';
		$latest[]=$entry;
	}
return $latest;
}
?>
%

I call the above with the following:

%
    require_once 'forum/joinfeeds.php';
    $latestfeeds=latestFeed(5);
%

to get the latest 5 posts.

Only in an internal site.

Just try it. Its very simple and works nicely. I use it exactly as posted here. Nothing changed.

There is no point in attaching a screenshot. Your implementation will look different.
My templating system just prints out entryes from an array. I'm on fatfreeframework (f3) and use bootstrap 3
My code looks like . You should get the idea

%HTML
<repeat group="{{ @latestfeeds}}" value="{{ @item }}" counter="{{ @ctr }}">

    <small>
     <p><a href="{{@item->link}}">{{@item->title}}</a></p>
     <p>{{@item->description}}</p>
     <p><i>Af {{@item->author}}</i></p>
          <HR class="feeds">
   </small>
   
  </repeat>
%

Its very simple.
Just save the joinfeeds.php file and then have your test.php be like this

%
<?php
    require_once 'forum/joinfeeds.php';
    $latestfeeds=latestFeed(5);

//Print some stuff from entries
foreach($latestfeeds as $feed) {

echo $feed->link," ",$feed->title," ",$feed->description
}

?>

%

I havent tested the above so experiment and use php.net for help. You have to take a look at the index.xml files to see what is available

:: @Jos added on 25 Jul ’16 · 18:27

Beware of path of require_once 'forum/joinfeeds.php';

:: @Jos added on 25 Jul ’16 · 18:29

And remember this is something that is perfect for me. It does not necessarely something for your setup, but its simple and easy to adapt to your needs. No need to a complex tools when something as simple does the job.