4. I'm actually a power user of Windows, Mac, AND Linux, and I know of the benefits of each, so this one is hard.
You may want to look for non-mainstream OSes then, like Haiku and 9front, or venture into the BSDs to see how they are different from each other and from GNU/Linux.
You'll be glad to know, FreeBSD is already on my list - I've got a book on it, and I want to know more. The Linux/BSD communities seem to follow some of the same cultural faultline as the FSF/OSI split.
I've also done some playing around with IBM OS/2 Warp. I'll have to find some more to try out, just for fun.
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