There is no, and won't be Aqua for any other platform. I'm just one guy in his bedroom, and Android keeps me fully (like, 200%) busy.
As for Windows mail apps, there is a great number of them these days.
Outlook, Windows Live Mail (nee Outlook Express), Windows Live Mail, Thunderbird, EmClient, IncrediMail, and probably a dozen others.
Note that mail apps don't sync with each other -- they each sync with the mail server, so you don't need something special that works specifically with Aqua.
