Credits module allows to have a system where people could pre-purchase ad placement/membership credits. This allows the customer to pre-purchase ad space at a savings and then use their credit as they place ads. Only a single credit card charge can take place for multiple ads (or future ads) without getting charged a service fee from the credit card company for each individual transaction.
The general idea is that it fools the search engine into thinking you have millions of pages and this increase your sites chances in showing up in the top pages of the search result. All you need to do is add the PHP code-snip to any of your page, edit the keyword list and let the search engine do its job.
Personal version has better optimization algo compared to the Lite version.
eZ xmlrpc is a PHP implementation of the XML-RPC spec. It enables distributed computing between different operating systems using different programming languages. The messages are XML-based and are transported via HTTP. It includes both the server and client classes and example code for the server.