PHP Twitter
PHP Twitter is a wrapper class around the Twitter API. Originally developed by David Billingham, it has been maintained, improved upon and cleaned up by Aaron Brazell with contributions from the Twitter development community.
PHP Twitter requires PHP 5.2 and the lib_curl module to be compiled into your PHP build. It also performs best when safe_mode is turned off.
The library can be downloaded here.
And of course, please report any bugs or issues you might come across.