RØDE has announced a beta firmware update that adds virtal devices to its RØDEcaster Pro II and RØDEcaster DUO mixing consoles.
In essence, this allows up to 4 individial applications running on your PC (only at present, Mac is due soon apparently) to be assigned to their own fader on the console. So for example, you can have Spotify on one fader, Skype on another, some game output on a third etc while still keeping a live mic on one as weell.
The video that RØDE has used to explain this in more detail is below.