Thinking about various operating systems and what makes them more or less preferable to others. So I'd like to put this question to you: If you could create a new OS with the best aspects of other existing systems — a "love child", if you will — what would it have? What are the things that set your favorite system(s) apart?

I'm phrasing the survey like this:

My ideal environment would have:

• the    (noun)    of Linux,
• the    (noun)    of Mac, and
• the    (noun)    of Windows.

Or:

My ideal environment would be:

•    (adjective)    like Linux,
•    (adjective)    like Mac, and
•    (adjective)    like Windows.

Feel free to use other systems (Plan9? VMS?) as you like, though I'm mainly interested in these "big 3".

For myself, I think my ideal environment would have:

• the simplicity, power, and FOSSitude of Linux,
• the sane and elegant UX of Mac, and
• the ubiquity (with all that entails — well, all the good stuff, anyway) of Windows.