Welcome to Snowdrop OS, a unique 16-bit real mode operating system for IBM PC architecture, designed and developed from scratch using x86 assembly language. This homebrew OS includes a variety of utilities such as a file manager, text editor, BASIC interpreter, and even a Tetris clone. Not to mention, one of the DOS games has been ported to run on Snowdrop OS. Users can also install Snowdrop OS on their hard disk, with source code available for modification. With versions ranging from single tasking to supporting virtual displays and multiplayer games, Snowdrop OS continues to evolve with new features like GUI framework, dynamic data structures, and multiple game options like Minesweeper and Hangman.
http://sebastianmihai.com/snowdrop/