I'm sorry for bringing this old thread up, but I was wondering if it would be possible, and if anyone would be interested in porting
Wolf4SDL to Rockbox. It's essentially an open source engine reconstruction of the Wolf3D engine, requiring the original game files to run properly, kinda like how Rockdoom/PRboom does for Doom engine games. The original version of Wolf4SDL relies on MAME OPL emulation code, which was GPL incompatible, but apparently the
Debian package of Wolf4SDL purged the non-free code and replaced it with Dosbox OPL emulation code, thus making this particular version GPL compatible.
The thing about Wolfenstein3D is that it has a relatively slower gameplay and a simpler control scheme that I believe it would make it far more playable on Rockbox-compatible devices than Doom will ever be. The game doesn't exactly require quick reaction times or avoiding enemies as swiftly as a Doom does, so it kinda feels like the ideal FPS to play on a smaller portable device.