The Horde framework adopted for Plesk
 
The Horde Framework provides a common structure and interface for Horde
applications (such as IMP, a web-based mail program).  This package is 
required for all other Horde modules.
The Horde Project writes web applications in PHP and releases them under
the GNU Public License.  For more information (including help with Horde
and its modules) please visit http://www.horde.org/.

WWW: http://www.horde.org