It's a week old news, but gzdoom officially went GPL.
https://forum.drdteam.org/viewtopic.php?t=7613

This is a major fucking game changer. It means Zandronum being under a GPL compatible license can can be used to play GZDoom. http://zandronum.com/
For the free culture enthusiast you could even use freedoom and the libre licensed mods.