like most games, this program is very poorly licensed - in this
case, so poorly that it is actually non-free - the code-base
includes a lone GPL file, but i could find no indication that
any files in the code-base are intended to be distributed under
any license

i also found a binary java .jar file in a directory by itself -
it is likely that file is im not sure if that is an important
file; but it is a clue that the developers do not think very
libre-friendly

unless someone can convince the upstream maintainers to license
it clearly, i would not touch it

the binary .jar file is (apparently) the apache2-licensed "gradle wrapper" - if that file is important, there is at least the CCS problem; because i had to guess what that program is and hunt down the source myself to find out what the license (maybe) is

About media content license: https://github.com/Anuken/Mindustry/issues/137

• https://github.com/Anuken/Mindustry/issues/5118
• https://github.com/Anuken/Mindustry/issues?q=license

that bug report only confirms my suspicion that the developer
is not very familiar with copyright and proper libre licensing -
that bug report was closed, based on the presumption that the
artworks are intended to be GPL-licensed, and therefore nothing
needs to be done - although incorrect, that is better than the
first suggestion, that all artworks would be given a
non-commercial license - at least the developer has expressed
the intention to license the entire code-base as GPL; but as it
is, the developer has not actually done so, and apparently does
not intend to do so

the "assets" are not the biggest problem - the problem is that
none of the files in that code-base specify any license -
therefore, it is 100% proprietary - if i though this program had
value to parabola, i would explain that to the maintainer, and
suggest how to license it properly - we did just that, last week
for the 'bombadillo' program; and the developer was very
cooperative, and made the suggested changes immediately