MAC OS X 10.6 (Snow Leopard), 10.7 (Lion),10.8 (Mountain Lion),10.9 (Maverick), 10.10 (Yosemite), 10.11 (El Capitan), 10.12 (macOS Sierra)
The Activation Server 5 is either hosted or can be installed on an own on-premise server.
The detail requirements are listed in the Activation Server 5 documentation.