This PHP Etherpad Lite class allows you to easily interact with Etherpad Lite API with PHP.
Etherpad Lite is a collaborative editor provided by the Etherpad Foundation (http://etherpad.org)

include 'etherpad-lite-client.php';
$instance = new EtherpadLiteClient('EtherpadFTW', 'http://beta.etherpad.org/api');
$revisionCount = $instance->getRevisionsCount('testPad');
$revisionCount = $revisionCount->revisions;
echo "Pad has $revisionCount revisions\n\n";

See it live here: http://beta.etherpad.org/example_big.php

Examples are located in examples.php and example_big.php.
examples.php contains an example for each API call.
example_big.php contains a UI for managing pads.

This example is the most commonly used, the example displays a pads text on the screen:

$padContents = $instance->getText('testPad');
echo "Pad text is: <br/><ul>$padContents->text\n\n</ul>";
echo "End of Pad Text\n\n<hr>";

Apache License

The Etherpad Foundation also provides a jQuery plugin for Etherpad Lite.
This can be found at http://etherpad.org/2011/08/14/etherpad-lite-jquery-plugin/