FreeDOS
Goal: complete, free, 100% MS-DOS compatible operating system with no enhancements or advanced features such as multitasking, protected mode operation, GUI. If you need advanced features in a free OS, try GNU/Linux. http://www.freedos.org/
DOS Games
Approximately 200 shareware and freeware games organized into fourteen categories. Associated utilities are also available for download, and free web-based e-mail is provided with the domain name @dosgames.com. http://www.dosgames.com/