The first of the complaints that some switchers have when switching to Mac OS X is usually that the green button on the window semaphore (as it is usually called) does not maximize taking advantage of all the space on our desktop, but adapts to the content of the window.
That is what RightZoom prevents, since with this program activated the green maximize button will always do so by forcing the program to fully expand, and it is something that many of us who prefer this behavior appreciate.
The program is totally free and does not consume any resources, so you can put it without fear on your Mac.
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