A few things to note:
If you use the default installation path for GOG games and you don't want to move the ROM files elsewhere, the script dragon-convert.py goes in C: > GOG Games > Double Dragon Trilogy > resources > game, and the script convert.py goes in C: > GOG Games > Raiden Legacy > roms.
Then run the scripts (requires Python), and the raw files will be placed in the folder mame inside the same folder as the scripts.
Just mind it seems the scripts can't convert the rfjet files from Raiden.

To make these raw files playable in MAME, I use the ClrMamePro method specified here:
https://docs.libretro.com/guides/arcade-getting-started/#optional-clrmamepro-tutorial
Just mind the program tries to generate all ROMs that have at least 1 of the files of the romset, but most ROMs aren't actually functional, so you'll have to dig the functional ones among them.

Forgot to mention, but in case the information is useful, the games included in Raiden Legacy and Double Dragon Trilogy can be compiled to MAME Current, and, from what I could test, the ROMs from Wizard Fire, BreakThru, Gate of Doom and Super Real Darwin are compatible with MAME 2003, but not MAME Current.

Heh, as someone else who took advantage of the excellent Ziggurat 2nd anniversary sale and got many of the Retro Classix games, here are my findings:

- Bad Dudes: Works normally in both current Mame and FinalBurn Neo
- Joe & Mac - Caveman Ninja: Works normally in both current Mame and FinalBurn Neo
- Joe & Mac Returns: Works normally in both current Mame and FinalBurn Neo
- Night Slashers: Works normally in both current Mame and FinalBurn Neo
- Two Crude: Works normally in both current Mame and FinalBurn Neo after renaming the twocrude.zip file to twocrudea.zip.
- Gate of Doom: Works with Mame2003.*
- Wizard Fire: Works with Mame2003**

All ROM files can be found in the game's NameOfGame_Data\StreamingAssets subfolder, sitting neatly inside a zip.

*This ROM is a weird combination of the US gatedoom.zip and the World darkseal.zip ROMs. Because of that it isn't detected as either.
If one wished to "complete" the ROM properly then one would need to *EITHER* replace the files gb_00.h12 and gb_05.j14 thus creating a complete Gate of Doom (US revision 4) ROM *OR* replace the files ga_01-3.h14 and ga_04-3.j12 thus creating a complete Dark Seal (World revision 3) ROM.

** This ROM appears to be a partial dump of the US wizdfireu.zip ROM. The file mas10 is only 512 KB instead of 1024 KB.
If one wished to create a "proper" ROM then one would need to replace the mas10 file with a complete one and then rename the zip file to wizdfireu.zip.

The following games I have not yet been able to purchase and test but I would at least expect them to run under Mame2003:

BreakThru
Heavy Barrel
Express Raider
Super BurgerTime
SRD - Super Real Darwin

Concerning the Double Dragon Trilogy, like _Auster_ already hinted, ALL THREE ROMs can be extracted from the game files and played using the current MAME*.

To extract them, first download the application Node.js to use with the script farmerbb created: https://github.com/farmerbb/RED-Project/wiki/Double-Dragon-Trilogy
https://gist.githubusercontent.com/cxx/81b9f45eb5b3cb87b4f3783ccdf8894f/raw/5b5e677d2d904071888fe7ea08a83c50ab9ba1cb/dotemu2mame.js

Create a new folder to copy/extract the following:
-All the files inside the Trilogy's "\resources\game" subfolder
-The node.js application files
-The dotemu2mame.js script.
Finally run the command:
node dotemu2mame.js .
(including the full-stop character).

The converted ROMs are saved as .zip files inside the folder:
- ddragon.zip: Works normally in both current Mame and FinalBurn Neo
- ddragon2.zip: Works normally in both current Mame and FinalBurn Neo
- ddragon3.zip*: Works in current Mame (but will display a LUA error)

*Double Dragon 3: For some reason, one of the files in this ROM, mb7114h.ic38 is not the original game file.
That is the reason why FinaBurn Neo rejects the ROM and also why Mame displays that LUA error during runtime.
If one wished to create a "proper" ROM then one would need to replace the current mb7114h.ic38 file with the game's actual file.

Thanks for the GitHub method for the Double Dragon Trilogy and both in-depth analysis!

Thank you, #1 UPDATED.

These are one-liners to extract the gog 1.1 roms on linux/mac/posix OS:
dd bs=1 skip=26867136 count=1048576 if=ZAMN_GP.exe of=gp.sfc status=progress
dd bs=1 skip=28346700 count=1048576 if=ZAMN_GP.exe of=zamn.sfc status=progress

Anyone knows if there is a rom file on Metal Gear?

From what I could gather from the game's forum here on GOG, as well as a Reddit post and some random threads, no. It seems it's a new version based on the MSX release, but no disk ROM was used. But if someone with the game wants to confirm, it'd be pretty helpful.

I see. Thanks.

Do source ports count? If they do, Aquaria can be turned into PSP and Switch ROMs.

Game page: https://www.gog.com/game/aquaria

The PSP version can be created with this tool:
http://achurch.org/AquariaPSPBuilder-1.6.678.tar.gz
The tool is only for Linux, but maybe it works on the latest update of WSL and on Mac with Unix's bash enabled.
And this version doesn't seem to work with emulators such as PPSSPP, since, according to someone on PPSSPP's Discord, some homebrews use uncommon API calls that may not be covered by the emulator yet, and this could be one of them. But it does work on an actual PSP, as well as the PS Vita since it is engineered to run PSP games (inherited hardware, partial PSP OS installation by default and capable of running the full PSP OS).

And it seems the Switch version can be created from this GitHub repo, but I can't test it right now:
https://github.com/dimag0g/Aquaria/tree/switch

Thank you!
The topic of this thread is "compatible with emulators" but I added Aquaria to #1 anyway. :-P

Hello. The mention about Wonder Boy in the OP only links dtgreene's find, and not the game's store page. Perhaps you'd want to link the store page as well?

https://www.gog.com/game/wonder_boy_the_dragons_trap

FIXED, thank you!