There are quite a few xmpp libraries that provide client functionality. The one I tried myself is XMPPHP. It’s usage is really simple. For example to send a message you would do something like this:

require_once('XMPPHP/XMPP.php');

$conn = new XMPPHP_XMPP('talk.google.com', 5222, 'user@gmail.com',
'password', 'xmpphp', 'gmail.com', $printlog = false,
$loglevel = XMPPHP_Log::LEVEL_INFO);

try {
    $conn->connect();
    $conn->processUntil('session_start');
    $conn->presence();
    $conn->message('friend@gmail.com', 'Hi!');
    $conn->disconnect();
} catch(XMPPHP_Exception $e) {
    die($e->getMessage());
}

I find this to be quite valuable. Who these days does not keep their IM live all the time? I imagine it’s like a cellphone. Meaning you can use it for many different services.

For example I developed a small application that checks if every one of my collegues is “Working on a task” in FogBugz and if not it sends an automated message to them to remind them that they should select a task they are working on. I also have a small tracker that tracks a local torrents network looking for high rated IMDB movies. I have an idea that it would be nice to integrate my tracker with GTalk so that it would inform me when a new episode of House MD is available or a new highly rated movie appears. The sky is the limit