3.1-tan is a fictional OS-tan character representing Windows 3.1 in the OS-tan parody franchise. She is usually depicted as a cute, anthropomorphized girl with a retro computer aesthetic, reflecting the early-era Microsoft operating system. As part of the broader OS-tan cast, she serves as a nostalgic and humorous personification of an old OS, often appearing in fan works that play on technology history, software quirks, and the personalities assigned to different operating systems.