Mac OS X was first released as Mac OS X Server 1.0, the commercial release of Rhapsody, and then released as Mac OS X Server for Cheetah, Puma, Panther, Tiger,

Mac OS X was first released as Mac OS X Server 1.0, the commercial release of Rhapsody, and then released as Mac OS X Server for Cheetah, Puma, Panther, Tiger, Leopard and Snow Leopard, before being released as a standalone update to Lion, and then hitting the App Store for $19.99 for all future releases.