I enjoy using Dropbox. It is a very easy syncing and backup tool, and it works everywhere. A few days ago the developer API was released. After a bit of wrestling with oauth, I completed a client library for PHP, and open sourced it (MIT licensed).

If you want to give it a shot, you first need to sign up for the developer program and get yourself your security tokens. Once that's done, you can install the library using:

pear channel-discover pear.sabredav.org
pear install sabredav/Dropbox-alpha

If that worked, you should be able to start using the API. The following example displays account information and uploads a file.

<?php

/* Please supply your own consumer key and consumer secret */
$consumerKey = '';
$consumerSecret = '';

include 'Dropbox/autoload.php';

session_start();

$dropbox = new Dropbox_API($consumerKey, $consumerSecret);

/* Display account information */
var_dump($dropbox->getAccountInfo());

/* Upload itself */
$dropbox->putFile(basename(__FILE__), __FILE__);

The script needs to be run in a browser, because you will be redirected to Dropbox to authorize access.

I hope people like the library, and if you have any suggestions, feel free to let me know. If you want to contribute, you can head over to the project site on google code.

If you haven't used Dropbox yet and want to try it, consider signing up through this link. If you do so, both you and my girlfriend get an extra 250MB space for free (and she really needs it).