Jack (the Jack Audio Connection Kit) is a low-latency audio server, written originally for the GNU/Linux operating system, and now with Mac OS X support. It can connect any number of different applications to a single hardware audio device; it also allows applications to send and receive audio to and from each other.

Jack is different from other audio server efforts in that it has been designed from the ground up to be suitable for professional audio work. This means that it focuses on two key areas: synchronous execution of all clients, and low latency operation.