Nexus 7 as a remote home controller
There are several different VLC remote apps available which will let you control audio/video playback on your PC when you are connected to the same network. It's probably not for the un-technical, but it does feel very cool controlling your "stereo" from the other end of your apartment. You will generally need to: 


Install VLC on your PC
turn on the web interface by going to (Tools>Preferences...>Show all (bottom left)>Interface>Main Interfaces>Web)
determine the IP address of your computer (Run command, Run
ipconfig)
Install a VLC remote app on your N7 (there are a multitude, try a
free one first)
Your VLC app will have somewhere to enter the IP address of the PC
    to be controlled


Note, if you can configure your router to assign a static IP to your PC you will save much re-entering of settings. 

I suspect a camera streaming to a static IP you could browse to from any device on your network should be possible, but I'm afraid I'm even less sure about the other stuff. That said; I suspect you might want to look into Arduino.