The tool is also known as PHPXMLRPC and is designed for ease of use, completeness and flexibility.
Speed and reduced memory footprint are not the main goals of the project.
This is not the same library as the one that is part of PEAR. They both share a common ancestry, since the PEAR version is a branch of the original phpxmlrpc library, now independently maintained.
This is not the library which can be compiled as an extension and has been bundled with php since version 4.1.0, either.
PHPXMLRPC or derivative versions are used in many open source projects, including Ampache, Xaraya, Drupal (only up to releases 4.6.2 and 4.5.4), PostNuke, b2evolution, nucleus cms, phpmyfaq, phpPgAds, phpgroupware, egroupware, TikiWiki, Civicspace (old release only) and MailWatch for MailScanner.