GeekOS is a tiny and simple operating system that was designed at the University of Maryland to show undergraduate students the fundamentals of operating systems. GeekOS was implemented and extended as a senior project at Anadolu University in 2006, and the new kernel was named OSman. While preserving the basic functionality available in GeekOS, OSman incorporates additional features such as multi- programming support, VESA graphics device driver, and a PCI Device Driver System Base. Despite having many nice features, the current version of OSman lacked crucial networking support. This book includes an implementation of a sample Ethernet device driver (for Realtek RTL8139) and a tandards-compliant, fivelayer TCP/IP Protocol stack implementation so that network applications can be deployed on a PC running OSman. A popular client- server network game called tic-tac-toe is implemented to demonstrate the communication between two PCs one running OSman and the other running Windows XP.