I'm OK with that about box. Here's the Readme.txt files

CB-Emu_Pro 2021 (MESSUI 0.175/0.190/0.220) - (C) 2021 by Franz Huber, Austria
MessChess for UCI/WB (MESSUI 0.220) - (C) 2021 by Franz Huber, Austria
MessExtra (MESSUI 0.220) - (C) 2021 by Franz Huber, Austria

*edit* it's more like this (may have mistakes, I made it rather quickly):

CB-Emu_Pro 2021
===============
based on MESSUI 0.175/0.190/0.220 (C) MAME Team
chesscomputer emulation (C) Cowering, Dirk Verwiebe, Franz Huber, hap, Jonathan Gevaryahu, Kevin Horton, Olivier Galibert, Peter Trauner, Sandro Ronco
chessboard user interface (C) Franz Huber, Ralf Schaefer
CB-Emu_Pro packaging and improvements (C) Franz Huber
special thanks to: Achim, anonymous, bataais, Berger, Sean Riddle, yoyo_chessboard

MessChess for UCI/WB
====================
based on MESSUI 0.220 (C) MAME Team
chesscomputer emulation (C) Cowering, Dirk Verwiebe, Franz Huber, hap, Jonathan Gevaryahu, Kevin Horton, Olivier Galibert, Peter Trauner, Sandro Ronco
chessboard user interface (C) hap
chess engine interface and plugins (C) Franz Huber, Sandro Ronco
MessChess packaging and improvements (C) Franz Huber
special thanks to: Achim, anonymous, bataais, Berger, Sean Riddle, yoyo_chessboard

MessExtra
=========
based on MESSUI 0.220 (C) MAME Team
chesscomputer emulation (C) Cowering, Dirk Verwiebe, Franz Huber, hap, Jonathan Gevaryahu, Kevin Horton, Olivier Galibert, Peter Trauner, Sandro Ronco
chessboard user interface (C) hap
MessExtra packaging and improvements (C) Franz Huber
special thanks to: Achim, anonymous, bataais, Berger, Sean Riddle, yoyo_chessboard