Regardless, it is a great game!
https://www.teeworlds.com/?page=docs&wiki=CompilingEverythin...
EDIT: though I've now realised that my reading comprehension is really lacking - he was referring to teeworlds, my bad!
"Teeworlds is a free, open source sidescrolling multiplayer-only shooting game. ... In December 2007, the source code was made available to the public under the terms of the zlib License."
https://en.wikipedia.org/wiki/Zlib_License