JACK2 (JACK Audio Connection Kit) is a C++ low-latency audio server for multi-processor machines that allows JACK client programs to process and route audio and MIDI data in a synchronous, sample-accurate and low-latency manner. Originally written for the GNU/Linux operating system, it also runs on various Unix platforms, Mac OS X and MS Windows.

JACK differs from other audio servers in being designed from the ground up for professional audio work. It focuses on two key areas: synchronous execution of all clients, and low latency operation.