AOE_CacheCleaner

Removes old cache entries in your Magento instance

Magento does not clear old cache entries by itself, therefore the cache will grow and slow down the whole application.

The Aoe_CacheCleaner will clean up old cache-entries by firing Mage::app()->getCache()->clean(Zend_Cache::CLEANING_MODE_OLD); in an user-defined interval.

Additionally you're able to clean up other caches as well, such as the Catalog Image Cache and the JavaScript/CSS Cache.

http://fbrnc.net/blog/2011/02/magento-automatic-cache-cleaner