This version of UNIX is called UNIX99 and is the brainchild of AtariAge forum member [mrvan] who originally wasn’t looking to develop a full operating system for this computer but rather a set of standard C libraries to help with other projects. Apparently the step from that to a UNIX-flavored OS wasn’t too big so this project was born. While the operating system doesn’t have a UNIX certification, it has most of the tools any of us would recognize on similar machines. The OS has support for most of the TI-99 hardware, file management, a basic user account system, and a command shell through which scripts can be written and executed.