OnSong has the ability to control devices using two technologies, OnSong Connect and OnCue. OnCue is built on Apple's Multipeer Connectivity Framework that allows your devices running OnSong to participate in a peer-to-peer network. This requires WiFi to be enabled, but you do not need to be connected to an access point. Due to limitations in the framework, this is limited to approximately 6 devices.
OnSong Connect works by making each device running OnSong a web server on the host network. This web server runs on the local network only and allows devices to communicate using web services. When you control other devices, the lead device acts as a web server, allowing other devices to download content from the library for temporary use. This means that you'll want to use the fastest device as the leader if you plan to connect many devices.
There is no set maximum devices so it's technically limited by the number of devices that can be attached on the network and how fast your devices can respond to OnSong Connect requests. We have tested OnSong Connect with 24 devices and it worked as designed.
Both OnSong Connect and OnCue can beam or stream content to devices that are nearby or attached to the same local network. These devices do not need to use the same account or be registered to the same user. Simply being on the network or nearby with networking enabled will suffice.