QuakeSpasm is a simple source port that primarily focuses on bug fixes
and backwards compatibility.

Its build system is a small Makefile which required a few patches in
order to compile on Redox. Currently, it compiles with both SDL1 and
SDL2. MP3 support is hard disabled since neither `libmad` nor `mpg123`
would compile. However, the default OGG container and Vorbis decoder
compiles fine.

Like Doom, Quake requires commercial assets or free replications in
order to run. I'm currently trying to write a small recipe for the
shareware files, but ironically that has more blockers than the source
port itself.

Beyond the lack of content, I think this port is good to go.