GNU Chess

Home: https://www.gnu.org/software/chess/, http://savannah.gnu.org/projects/chess/
Media: https://en.wikipedia.org/wiki/GNU_Chess
State: mature, inactive since 2017
Download: http://ftp.thunix.net/gnu-ftp/chess/
Platform: Windows, Linux, macOS
Keyword: game engine, strategy, chess, content open
Code repository: http://svn.savannah.gnu.org/svn/chess/ (svn), http://cvs.savannah.gnu.org:/sources/chess (cvs)
Code language: C++
Code license: GPL-3.0
Assets license: None
Developer: Chua Kong Sian, Stuart Cracraft, Lukas Geyer, Simon Waters

Can be used together with a graphical frontend such as XBoard. Windows binaries via https://sourceforge.net/projects/gnuwin32/

Building