A multithreaded, multi-user SQL database management system (DBMS) having more than 11 million installations. This program acts as a server that provides multi-user access to a number of databases.
It is one of the most popular for web applications and also acts as a database component of the BAMP,MAMP,LAMP,WAMP platforms and for tools like Bugzilla which is an open-source bug tracking. Wikipedia, a famous user online encyclopedia, uses a MySQL database.