Open source projects used to in Wikipedia

Wikipedia is a multilingual, collaboratively edited encyclopedia. It is one of the busiest site in the world. It has more than 8 million articles and accessed by millions of users around the world. This article briefly discuss about the open source software used in Wikipedia.

All of its servers primarily runs on Ubuntu Linux http://www.ubuntu.com/

PowerDNS helps in Geographic Load Balancing. It has 3 datacenters and based on the client IP address the request will be processed by nearest cluster. http://powerdns.com/

Linux Virtual Server (LVS) used as an internal load balancer to distribute MediaWiki and Lucene backend requests. http://www.linuxvirtualserver.org/

Squid helps to do HTTP reverse proxy caching. It delivers the pages faster. http://www.squid-cache.org/

MediaWiki is the main application which is written in PHP. http://www.mediawiki.org/

Metadata and user information is stored in MySQL database. http://www.mysql.com/

Memcached distributed object caching system is used to cache database results. http://memcached.org/

Lucene is used to perform full text search. http://lucene.apache.org/

Ganglia used to monitor the servers. http://ganglia.info/

Lighttpd is a high speed Webserver used to deliver images from image server. http://www.lighttpd.net/

Apache most popular and widely used web server used to server HTTP request.http://httpd.apache.org/

Reference:
Wikimedia Architecture