This module allows you to create "virtual video devices" normal (v4l2) applications will read these devices as if they were ordinary video devices, but the video will not be read from e.g. a capture card but instead it is generated by another application. this allows you for instance to apply some nifty video effects on your Skype video... it also allows some more serious things (e.g. I've been using it to add streaming capabilities to an application by the means of hooking GStreamer into the loopback devices).
DKMS version is in the AUR.