VAC is intended to connect several audio applications together in real time. It's like a sound card with hardwired input and output: when an application sends an audio stream to a virtual cable, other applications can record this stream from the other cable end. Thus, you can record and process output of almost any audio application by almost any other audio application.
What's new in this version:
Version 4.10 has added IPrefetchOffset interface support (more stable audio in XP/Vista/Server 2008/Win7). Added a workaround to avoid Skype freezing and to stabilize streaming in heavy load cases.