The "EXP" executable format used by the TOWNS OS RUN386.EXE DOS extender is simple enough to layout with a linker script and raw binary output, so I managed to make a "hello world" executable using standard ELF i386 Linux gcc, nasm, and ld and run it in the Tsugaru emulator.

The previous owner of this FM TOWNS UX20 thoughtfully removed the CMOS battery from the computer to keep it from exploding and damaging the electronics inside, but unfortunately, TOWNS OS uses the CMOS settings to remember whether you have a hard drive and what drive letter(s) to use for it, so without a battery, you have to reconfigure the hard drive every time you power up. So I opened it up to put a new battery inside. There isn't a lot of documentation on the English Internet about taking these machines apart, so I'll walk through how I did it here. Like anything with a CRT in it, be careful about extremely high voltages that may still be charged inside!

By the same person who ported DOOM and Celeste Classic: https://bcc.hatenablog.com/entry/2023/04/09/235722