As announced a few month ago, there is a new REST client for PHP developers (restclient-php). Now we can proclaim the first stable release of version 1.0.0. This PHP library is really easy to use and supports all functions of the BibSonomy REST API. It also provides an integrated CSL-processor (citeproc-php) that helps you to render bibliographies.
In addition, there is a tutorial for the use of restclient-php which contains some useful examples scripts.
We hope that helps you to develop your own App for BibSonomy.
Happy tagging,
Sebastian