Yes, the Quartet USB audio connection can be plugged directly to the USB port of any Mac with OSX 10.6.8 or higher, without installing any additional drivers or software, and fully function as an Audio I/O device.
All of the Front Panel controls (Mute, Dim, Sum to mono, Input/Output levels) are fully functional without installing any software.
You will need to install the latest Quartet installer package from Apogee's site for full access to functions such as toggling input source (ex. from Microphone to Instrument), enable speaker sets, low latency monitoring, etc.
These functions and many more are accessible through Apogee's Maestro 2 Application (Automatically included with the Quartet Software Installer)