Mac06 (pronounced "Mac oh six") is a POSIX-compatible environment (library and a system kernel) for the MacOS. Its features include a UNIX-like file system using HFS with full Finder integration; POSIX libc.a and #include headers; a curses library; a POSIX shell; many basic UNIX commands, such as cd, cat, find, fgrep, etc.; a software development environment; and sockets for TCP/IP. Mac06 is a useful environment for learning UNIX as it runs as an application on top of the MacOS, allowing the user to switch between UNIX and the MacOS without rebooting. Currently at version 0.99, Mac06 will become a shareware application costing 20 dollars at its 1.0 release.