Postfix, Subversion, and other applications use it. It's embedded and doesn't draw attention to itself unlike a server application. There are about 200 million

Postfix, Subversion, and other applications use it. It's embedded and doesn't draw attention to itself unlike a server application. There are about 200 million installs of it. Also note that probably SQLite is a more popular relational database than MySQL (it ships with every copy of OS X and every iPhone, for instance), although I don't have any data on that.