Did you know that the concept of "OS-tan" has existed way before even ME-tan was made?
Take OS Idol Win-chan as an example. Win-chan's earliest appearance in media seems to be from a promotional CD by Enterbrain, which dates back as early as October 1998. This would mean that Win-chan predates Me-tan by almost 5 years. It's not specified what Windows version she represents.
Another example can be Magical Toko-chan who is from around 1999. She seems to represent BSD, has a theme song called "Rainbow Holy☆Trident" and has a sister that represents Solaris.
There is also also another "Wintel Miku" although there’s little art of her. She seems to represent WindowsNT4.0/95/98 and was created as the creator was inspired by Mgaical Toko.
Besides Win-Chan, Magical Toko, Solaris-Chan and Wintel Miku all have sites dedicared to them!
Toko: http://tokochan.haun.org/
Solaris-Chan: https://pony.tail.net/toko/sol.html
Wintel Miku: https://web.archive.org/web/20000226063048/http://www.quark-jp.co.jp/~hide/DirectGirl/index.asp
Also fun fact, Win-chan was made by the creator of Sgt.Frog and the concept designer for Kemono Friends, Yoshizaki Mine! This can be seen on his profile for his site here: http://mnet.nicomi.com/MINEprofile/YOSPRO.html