Hello.
ImpressPages CMS - php 5.3.X (
http://www.impresspages.org) - not require PDO Extension
Automne CMS , php 5.2.X (
http://en.automne-cms.org/web/en) - this is good alternative , but needs some things;
64MB of memory for PHP scripts (depending on the number of installed PHP extensions: further extensions require more memory).
PHP PDO Extension installed with MySQL driver.
PHP CLI Module available on the server with "system" and "exec" functions to use background tasks.
PHP GD Extension GD (needed to works on images) with libraries JPEG, GIF and PNG.
PHP MbString Extension.
PHP "safe_mode" option disabled.
PHP installed as an Apache module (CGI version offers lower performance but works).
Zlib extension (allow HTML compression).
PHP "magic_quotes_gpc" option disabled.
Apache must have the right to create and edit all Automne files on the server to use automatic installation and update system. Without that, some parts of the installation and updates should be done manually.
An opcode PHP cache like APC or Zend optimizer is a plus for performance purposes.
( This 2 are drag&drop CMS).