CoreChess GUI

zentropy GUI : https://github.com/FireFather/zentropy
Executable .exe in folder:
zentropy-master\zentropy-master\Zentropy\Bin\x64\Release

Jerry chess:

https://github.com/asdfjkl/jfxchess/releases/tag/v4.2.1

BanksiaGUI (Windows/Linux/Mac):

https://banksiagui.com/

Eschecs (simple chess GUI for playing against engines. No analysis. Windows/Linux.):

https://github.com/rchastain/eschecs/releases/tag/5.0.6

Python Easy Chess GUI (Windows):

https://github.com/fsmosca/Python-Easy-Chess-GUI/releases/tag/v1.18.2

Crafty Chess Interface (Windows):

https://sourceforge.net/projects/craftychessinterface/

R-Chess (This chess program is meant for beginners and you cannot use chess engines other than the one that comes with it. There is no analysis either. On hardest difficulty (professional) ELO is under 2000 but you still need to pay attention to win. I would say it is a good sparring partner for players rated between 1600-1850. There is a portable version available on the download page. The program is available for Windows and Android (I have not tested the Android version).

https://www.freeware-schach.de/

BelrdChess GUI (Windows):

https://github.com/Bernton/BerldChess

Chess Hero (This one is a simple training tool. You can't directly play a game against the engine, instead you feed the program with PGN files and it will bring up random positions for you to find the best move. I find it quite fun I recommend that you change the included Stockfish engine to the latest version. Available for Windows (Installer and portable):

http://innokuo.altervista.org/chesshero.html