a fun little project, which is remotely useful for if you are paranoid
in public places on your laptop:

tunnel vision (win32)

not sure what I'd do with it, let me know what you think.
left control+right alt makes the circle smaller
left control+right control makes it bigger
left control+left alt+right control+right alt quits it (as does selecting 
it on the taskbar and hitting alt+f4)