The OS-tan are an Internet phenomenon or meme that originated within the Japanese Futaba Channel. The OS-tan are the moe anthropomorphism/personification of several operating systems by various amateur Japanese artists. The OS-tan are typically depicted as women, with the OS-tan representative of Microsoft Windows operating systems usually depicted as sisters of varying ages.
Microsoft XP-tans Homeo - Windows XP Home version (male)
Homeko - Windows XP Home version (female)
XP-tan - (Female)
XP-kun - (Male)
Vista-tans Vistake
Chiivistan
Visbou
Windows 2000-tans 2k-tan - Windows Server 2000 Professional
saba-tan - Windows Server 2003
me-tan - Windows Millenium Edition
Apple Linux-tan - Linux, Distribution Specific openSUS, Fedora
Ubuntu
Debian
Gentoo
Mandrive
Slackware
¹Unlike the more popular windows os-tans, the Apple os-tan are mostly without a name but can be narrowed down by searching for something like os9
² Linux differs from the operating systems in that it comes in many distributions which all have a different company or group of people behind them.
There is linux-tan to represent all of the distributions who resembles the linux penguin/mascott Tux.
But some distributions have a linux-tan of their own as well, there however are major differences between works from different artists.
Further information
The OS in OS-tan, stands for Operating System. The software used that enables other software to access your hardware.
The '-tan' in OS-tan is simply a mis pronunciation of '-chan', mainly used to to make it sound cuter.
The OS-tans are the moe anthropomorphisation of these operating systems, and thus besides being moe have some of the characteristics of the operating Systems. For example the OS-X os-tans are usually displayed with nekomimi as their codenames are cats. Windows os-tans (the older ones) usually have a blue outfit as the default windows background is blue.
The operating systems are not the only applications with moe representations, there's also firefox-ko, thunderbird-ko, opera-tan, lady macafee and many others.. like the not so moe dr.norton who's just an old perv