XBoard
XBoard is a chess frontend for the X Window System, which runs on Unix / Linux systems. For Windows, there is a corresponding port named WinBoard. Originally, the program was developed by Tim Mann, but newer versions developed by modifications of HG Muller and others. With XBoard two people can play against each other, but only on a chess server.
Protocols
For special celebrity the protocol is reached, the front-ends use to communicate with the chess programs. This, called Chess Engine Communication Protocol ( CECP ), is next to the newer Universal Chess Interface (UCI ) is still the standard in this area.