http://uploaded.net/file/4e8kfrwn
I use this called Gammacontrol.exe.(v1.0.3.1)
I got from a German H.L.Counterstrike forum long time ago.
It has info in panel on front of app,
crt+alt +1 for darker
crt+alt +2 for brighter.
and it has a little tick box ,if u want it to autostart after windows bootup.
It's a few kb in size and does the job well.
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SIDENOTE:
Also Google for ' superf4 '
It's another small tray app.
It has a kill button for when a game freezes and u can't alt-tab out of it.
It has two ways to kill the frozen game.
It's still been worked on ,so isn't 100% perfect yet.
But it's got me out of trouble a few times.