Netjack is a Realtime Audio Transport over a generic IP Network. It is fully integrated into JACK.
When you transport Audio Signals over a Network, you will always have the problem, that two Computers are bound to two different Sample Clocks. The other Network Transports face the Problem of compensating for the drift between these Sample Clocks. This is very hard to do.
NetJack works around this problem, by syncing all Clients to one Soundcard. So there will be no resampling or glitches in the whole network. As long as there is no packet loss. Packet loss can not be compensated.