Using FaceTime and Skype (both open at the same time) I would like to use both Skype and FaceTime at the same time (not while calling just having them both open).

When I start FaceTime it switches on the camera and keeps it on. If I hide the application the camera seems off (green LED is not on).

But if I use Skype the camera is not available since (even if the LED is off) the camera is still in use by FaceTime.

Is it possible to have FaceTime on waiting for calls without blocking or using the camera? In theory the camera is only needed during calls.
There is an app for that :)

ManyCam will allow you to use the iSight camera over multiple applications. I haven't had the chance to test it myself, but according to the app description, it should work just fine.    

Some customers complain about a slow Mac, some don't. So please give feedback about this app. 

EDIT:
CamTwist should do the same.