I ported dhewm3 (a Doom 3 source port) to the Switch.
Right now this is more of a proof of concept kind of thing rather than a fully playable port, as performance is pretty abysmal (20-30 FPS on average with shadows disabled, less with shadows enabled).

Github repo: /fgsfdsfgs/dhewm3
Latest version: 0.1.0 (Sep 30, 2018)
Download link

Warning: Spoilers inside!

Features:

• hardware accelerated rendering;
• sound/music through OpenAL-Soft ("EAX4.0" effects are also supported);
• half-assed analog controls.

To install, unzip dhewm3nx_v010.zip to SD card root, then copy over pak000.pk4 through pak008.pk4 from the base folder of your PC Doom 3 installation to /switch/dhewm3/base/.
Your Doom 3 installation should be patched to v1.3.1. The Steam version is already patched, the files are in Steam/steamapps/common/Doom 3.
If you're using data files from a non-English version of the game and your base folder has additional zpak###.pk4 files in it, also copy those over to /switch/dhewm3/base/.
Doom 3 BFG files are not supported, someone would need to port RBDoom3BFG for that.
For more information read the README and this FAQ.

Some notes:

• this will only run correctly through NSP hbmenu or if you make a standalone NSP out of it or if you use a game/demo as a donor title on Atmosphere (i.e. as a regular app), if you run it through Album hbmenu (i.e. as an applet), it will run out of memory and crash as soon as you try to load any map;
• in the main menu you can control the cursor with the Right Analog, triggers act as mouse buttons;
• you can also use the touchscreen to control the main menu;
  
• left analog is a little wonky in game after loading, jiggle it for a second and it'll work;
• multiplayer is borked, selecting it will crash the game;
• loading and saving times are pretty long;
• by default, Video Quality (which is essentially texture detail) is set to Medium and shadows are disabled, but you can tweak any settings (except resolution) to your liking, some of which may require a restart;
• currently only 720p is supported;
• sometimes after loading a map your gun viewmodel will disappear, this is fixed by going into Options -> Game Options and toggling Show Gun Model off and back on, I have no idea why this happens at all;
• if you want massive amounts of "atmospheric" reverb on most in-game sounds, you can turn on "EAX4.0 HD" in Options -> System (not sure if it's even supposed to sound like this);
• Resurrection of Evil is not currently supported by the release NRO, you can use this separate build that can only run RoE if you want to play it;
• if the game crashes for no apparent reason on startup, probably with a 2011-0301 error, try disabling any extra sysmodules you have loaded (sys-ftpd, xorplay, etc);
• if you're using data files from a non-English version of the game, you can change the game language by changing the values for in_kbd and sys_lang in dhewm.cfg from "english" to e.g. "spanish";
• as usual, if you have exFAT, better quit the game using the "Exit" option in the menu instead of just killing hbmenu.

Credits:

• dhewg and Daniel Gibson for dhewm3;
• fincs, Armada651, Subv and probably others for their work on the OpenGL/mesa/libdrm stuff;
• some nice people in the ReiSwitched Discord and #switchdev for help and testing;
• id Software for Doom 3.