What addon causes this?

[Railin]

This morning when I logged on this all of a sudden popped up in the middle of my screen. All the frames are movable. It includes some unit frames (in the middle) and a random skillbar and a couple other transparent boxes.

[Bornabe]

It's whichever Unit Frame addon you're using. Are you using someone's compilation? I don't recognize that UF mod directly, but can try to help you locate which one it is.

[Fuzzywuzzy]

Could be panels placed behind some addons you have removed, but leaving panels there.

[Jagger_]

I believe it's Feral by Night.

[Bornabe]

It does look exactly like that addon. Maybe a setting allowing you to move it's frames is unlocked? An option like that'll show all the boxes you can move, just like it's doing on your screen now.