=== [http://pecl.php.net/package/memcache/ Memcache] ===
This has been a great app for us, since it's simple and effective. Any data that is access often and can be hashed is a good candidate for memcache.
* In AMOv2 we stored the complete page output in memcache using the URL as a the key
* In AMOv3 (remora) we're storing db query results using the query as a key
* [http://en.wikipedia.org/wiki/Memcached Additional Memcache Info]