After some digging I found that no sourcecode was ever ported to ARM based unix systems?
Having no experience in porting developer source code to certain systems, could theoretically someone use the supposed "source files" on this page, of which i'm uncertain if it is ut99's source although it says "Unreal Tournament public source v432 for the orginal Unreal Tournament", to make an ARM 32bit or 64bit Unix port for the Raspberry Pi? To play it not using box86 and having framerates higher than 25
