What is "os-tan"

The OS-tan is 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.

Though initially appearing only in fan work, the OS-tans proved popular enough that Microsoft branches in Singapore and Taiwan used the OS-tan concept as the basis for ad campaigns for Internet Explorer and Microsoft Silverlight, respectively.