Lion
Created by Chris Welty. Lion is an Othello client to connect and play on the CGS server.
THe ODK source code is also available, which can connect your C Othello program to the GGS server in 15 minutes.
Note: GGS has moved to skatgame.net. Please read here for more details.
Downloads: Lion, ODK Source Code
Mimosa
Created by Kevin Wong. Mimosa is a GUI client for the CGS.
Downloads: Mimosa
SGF File Format(FF[4])
The Smart Game Format, or SGF, is a popular file format used to store game records of board games for two players.
Download: SGF FF[4]