Undertale

Undertale (PC, 2015) has an open-source reimplementation, fachinformatiker/undertale, and 5 other public projects, including code that decompiles almost back to source.

Data checked 2026-10-12 · unbaked registry

PortMaster GameMaker

Projects

undertale

ReimplementationGameMaker Studio247 starspushed 2019-02-09no license

Undertale src code

development halted; status unplayable

Xbox One

Readable bytecode126 starspushed 2025-09-04custom license

UNDERTALE Xbox v1.13X Decompilation

ut10-decomp

Readable bytecode3 starspushed 2026-04-02no license

A decompilation of the UNDERTALE 10th Anniversary game (using GameMaker Studio 2024.2.0.163)

UndertaleModTool (GML bytecode decompiler/editor for data.win)covers 4 games

Readable bytecodeGameMaker Studio 1.4 VM bytecode -> UTMT decompiles all GML; recompil…2,077 starspushed 2026-09-07GPL-3.0 licenserelease 0.9.2.0

The most complete tool for modding, decompiling and unpacking Undertale (and other GameMaker games!)

GitHub

PortMaster port 'undertale'

Readable bytecodeGameMaker (data.win) run on ARM Linux via gmloader/gmloader-next (And…

Commercial/indie or freeware GameMaker game packaged in PortMaster (main) as undertale, updated 2025-08-01; needs user game files

Undertale/Deltarune decompiled source

Readable bytecode

decompiled GML of Undertale demos and Deltarune Ch3 (patch-based distribution)

What you need

You need your own copy of the game: these projects ship code only.

Same toolchain

GameMethodYearStarsLast push

DOSDoomSource releaseMatching decomp+8199320k2026-10-12 DOSCommand & ConquerSource releaseReimplementation+2199518k2026-10-12 WEB2048Source releaseReimplementation+1201413k2026-08-19 PC2048 PlusReadable bytecode13k2024-10-24 PCMinecraft: Java EditionReimplementationSource port+220117.6k2026-10-11 PCBattle for WesnothSource release20056.9k2026-10-12 DOSQuakeSource releaseMatching decomp+419966.1k2026-10-12 PCThe Elder Scrolls III: MorrowindReimplementation20026.6k2026-10-12

More on PC

GameMethodYearStarsLast push

PCMindustrySource releaseAgent environment201929k2026-10-11 PCosu!Source releaseReadable bytecode+1200719k2026-10-12 PCCommand & Conquer Remastered CollectionSource release202021k2025-01-16 PCRollerCoaster Tycoon 2ReimplementationAgent environment200216k2026-10-12 PCDune 2000Reimplementation199818k2026-10-11 PCAge of Empires IIReimplementation199914k2026-10-03 PCCataclysm: Dark Days AheadSource release201313k2026-10-12 PCCivilization VSource releaseReimplementation201011k2026-10-12

Found via osgameclones.com/, SubmitGame/awesome-decomp-games, madpai/game-decomp-compendium/blob/main/skills/g, CharlotteCross1998/awesome-game-decompilations, search?type=repositories&q=%22decompilation+of%2

GitHub data checked 2026-10-12. Notes are summaries from the research pass; the project pages are the authority.