4os is the first Operating System written completely in Forth ForthOS is a complete, standalone operating system for the PC.

http://web.archive.org/web/19991022233047/www.itvc.com/Technology/4os.htm http://www.forthos.org/ 4os is the first Operating System written completely in Forth What do you mean by complete? How can I get a copy? What services are available? Why Forth? 4os is a complete networked information appliance operating system All the system services needed for a networked device have been implemented. The network stack is complete and written in ANS standard Forth (IP/UDP/TCP/SLIP/PPP/DNS/TFTP). 4os is only available from The iTV Corporation Currently 4os is only available as part of iTvc's Internet products. Individuals interested in licensing the operating system separately should contact us. 4os provides extensive services to the application developer System has task, memory management, objects and structs, display device, keyboard and remote control devices, flash file system, windowing, font, user interface widgets, and exception handling services. 4os was implemented in Forth because it requires less from the processor and product A complete Internet system (OS, live Forth system, network stack, flash file system, GIF and JPEG decoder, fonts, network support applications, email and browser customer applications) requires less than 1/2 megabyte of program memory. With boot compression (comes standard, takes about 1 second) that system fits in a 128Kbyte ROM.