System 7 and earlier
The version of System Software introduced with the Mac Plus
The version of Mac OS released shortly after Steve Jobs' return
Codename for the second version of Mac OS X
What is Mac OS X 10.1 Puma?
The naming scheme for all Mac OS X versions until Mavericks
The naming scheme for all OS X versions since Mavericks
The year System 6 came out
The first version of Mac OS to support Intel processors
The last version of Mac OS X to support PowerPC (not Intel) processors
What is 10.5 Leopard?
The latest version of macOS as of October 2019