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400+ real apps (44GB), Over 995 million downloads
New: PortExpert (Oct 12, 2021)
KatMouse is a useful freeware program that causes the mouse scrollwheel to work on the windows under the mouse rather than the active windows. I believe this mimics the MacOS behavior. The program is here: http://kickme.to/KatMouse
Well it's freeware, and the homepage says at least one of the registry entries needed to be dealt with, but I couldn't find an actual license. Might be included with the download, though.
This looks like a good alternative: http://www.deskangel.com/deskangel/
... and it's portable too!
Here's another one: http://www.softwareok.com/?seite=Microsoft/AlwaysMouseWheel