Download of ScreenDimmer 1.4 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This Mac app was originally designed by Atlas Wegman.
From the developer:
ScreenDimmer is the brightness utility OS X has been missing. With support for multiple monitors, intuitive slider behavior, and always available key shortcuts it is a simple yet comprehensive solution to a problem many Mac users struggle with. It is capable of controlling the brightness of up to three monitors, independently of each other. It gives you complete, fine grained control over all your external displays.