Memcached is a free & open source, high-performance, distributed memory object caching system, intended for use in speeding up dynamic web applications by alleviating database load. Danga Interactive developed memcached to enhance the speed of LiveJournal.com, a site which was already doing 20 million+ dynamic page views per day for 1 million users with a bunch of webservers and a bunch of database servers
Memcached is an in-memory key-value store for small chunks of arbitrary data (strings, objects) from results of database calls, API calls, or page rendering.
Memcached is simple yet powerful. Its simple design promotes quick deployment, ease of development, and solves many problems facing large data caches. Its API is available for most popular languages.
The popular sites which are using memcached are LiveJournal, Wikipedia, Flickr, Twitter, Youtube, WordPress, Craigslist and more.
Download : http://code.google.com/p/memcached/downloads/list
License: New BSD License