Database result serialization.
Cache Money stores all database result sets on the filesystem as serialized data, by using the oft-neglectged wp-content/db.php to extend the normal $wpdb class. Result sets will be updated as needed on a user by user basis when they do actions that perform update queries.
Please note that this is not a full scale page cache, like WP-Cache or WP Super Cache, although this will work just fine in conjunction. Cache Money is meant for sites with constantly changing content, where a full cache may not be suitable.
Tested with WordPress and WordPress MU 2.8.0 ~ 3.1 Requires PHP 5, like all good PHP apps.