TJchess, TJchess10x8, TJshogi, and TJxiangqi are original and free engines for playing chess and variants of chess. If you are not familiar with chess engines, Wikipedia has a good description. I started working on TJchess as a hobby in January of 2006, and have worked on it from time to time since then. Later, I started working on TJchess10x8, TJshogi, and TJxiangqi. They started out as really quick ports of the original TJchess code to other variants. Besides normal chess, TJchess itself is also able to play variants crazyhouse, loop chess, bughouse, and Fischer random chess.
Online computer chess articles and discussion forums have very been helpful in giving me ideas on how to get started and how to improve TJchess. I haven’t spent any time studying open source chess engines yet, but may do that eventually. All of the engines on this site are not based on any other program, and do not use any other engine’s source code or libraries or parameter values, including all protocol (WB/UCI) code, search, evaluation, overall framework, etc.