On November 20, 2025, Microsoft’s Open Source Programs Office, Team Xbox, and Activision formally licensed the source code for Zork I, Zork II, and Zork III under the permissive MIT License. The repositories were already publicly preserved; the significant change is official authorization for reuse. The release covers historical source collections, not the complete commercial games, Zork trademarks, packaging, or marketing assets.
What Microsoft released
The announcement applies to three existing historicalsource repositories:
| Game | Original commercial year | Repository |
|---|---|---|
| Zork I: The Great Underground Empire | 1980 | github.com/historicalsource/zork1 |
| Zork II: The Wizard of Frobozz | 1981 | github.com/historicalsource/zork2 |
| Zork III: The Dungeon Master | 1982 | github.com/historicalsource/zork3 |
Each collection contains ZIL source, compiled or partly compiled historical files, development-era material, and documentation where available. The repositories identify the games as Infocom interactive-fiction works associated with Marc Blank, Dave Lebling, Bruce Daniels, and Tim Anderson.
These are archival source collections rather than modern software projects. They do not promise a maintained build system, installer, reproducible build, or an exact reconstruction of Infocom’s final production environment.
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Why three games came from one larger Zork
The original mainframe game—often called Dungeon or the mainframe version of Zork—was too large for early home computers. Infocom divided the design into three commercial releases and used the Z-Machine, a virtual-machine architecture that let story software run on many different computer platforms.
The source release therefore concerns the commercial microcomputer trilogy, not every game that later used the Zork name. Beyond Zork, Zork Zero, Return to Zork, Zork Nemesis, and Zork: Grand Inquisitor are not automatically covered.
The source was public before the announcement
The historicalsource repositories had been publicly available for years, with the source described as anonymously contributed snapshots of Infocom’s development system. Microsoft did not present a wholly new source dump on November 20, 2025. Its contribution was the formal MIT licensing grant, made through upstream pull requests to those existing repositories, together with official recognition involving Microsoft, Team Xbox, and Activision.
That distinction matters: preservation access existed earlier, but clear permission to reuse the covered code now comes from an explicit license.
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- Created in collaboration with movie trilogy co-writer and producer Bob Gale
- Features original movie cast members Christopher Lloyd ('Doc' Brown), Tom Wilson (Biff Tannen), Claudia Wells (Jennifer Parker), and in special cameo appearances, Michael J. Fox as McFlys of the past. And the future!
- Includes in-game access to exclusive content: a behind the scenes video featuring interviews with Bob Gale, Tom Wilson, members of the development team, and AJ LoCascio - the voice of young Marty McFly
- Your choices and actions change to story around you
- A classic Telltale game that lead to their breakout hits The Walking Dead, The Wolf Among Us, Game of Thrones, and Tales from the Borderlands
What the MIT License permits—and what it does not
For code covered by the repository license, MIT generally permits people to inspect, copy, modify, compile, and redistribute the software, including in educational or commercial projects. Derivative distributions must retain the applicable copyright and license notices.
The grant is not a blanket release of Zork intellectual property. Microsoft specifically excludes commercial packaging and marketing materials and does not grant rights to Zork trademarks or brands. Developers should also treat the following as separate rights questions unless a particular file is clearly licensed:
- Zork names, logos, and other trademarks.
- Box art, manuals, maps, feelies, and promotional materials.
- Original story text, characters, and other expressive content outside the licensed code.
- Files with different ownership or licensing terms, including possible third-party contributions.
A technically valid fork can therefore still create trademark, copyright, attribution, or consumer-confusion problems if it presents itself as an official Activision or Infocom product.
ZIL and the Z-Machine
The games are written in ZIL, Infocom’s Zork Implementation Language. The repository documentation describes ZIL as a refactoring of MDL (also known as Muddle), a language related to Lisp. ZIL source was compiled for the Z-Machine, which executes portable story files rather than a conventional modern executable.
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Historical files in the repositories include formats such as .zil, .zap, and .zip. The original Infocom compiler and production build environment are not available as ordinary modern tools, so compiling today requires community tooling and may require adjustments.
How to play the finished games today
Buy the preserved commercial releases
For readers who simply want to play, the least technical route is The Zork Anthology on GOG. The listing describes a DRM-free Windows release, an optional GOG Galaxy client, and an offline installer. It includes Zork I, Zork II, Zork III, Beyond Zork, Zork Zero, and Planetfall.
The page showed a $19.96 sale price against $23.96 on August 18, 2026. That is a time- and region-sensitive observation, not a permanent price. This is a commercial re-release of finished games, not a modern remake, and its stated platform information is Windows-oriented.
Why the repositories are not a free game download
MIT-licensed source is not the same thing as a ready-to-run commercial package. The repositories contain historical build inputs and artifacts, but a player still needs a compiler, the right story-file format, and a Z-Machine interpreter. Existing binaries in a repository are historical artifacts and do not prove that an identical build can be reproduced.
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How to compile a source tree
Microsoft points readers to the community-maintained ZILF compiler and a Z-Machine interpreter such as Windows Frotz. The Zork I README says there is no known official Infocom compiler that can rebuild the final interpreter program, while ZILF can compile the files with minor issues.
Microsoft’s example is a Windows-oriented path, not a universal recipe:
"%ZILF_PATH%zilf.exe" zork1.zil
"%ZILF_PATH%zapf.exe" zork1.zap zork1-ignite.z3- Install or obtain ZILF from zilf.io and set
ZILF_PATHto its actual installation directory, or replace the variable with a full executable path. - Work from the repository’s documented source files; filenames and targets can differ among Zork I, II, and III.
- Run the compiler and assembler commands, adapting Windows path syntax for another operating system.
- Open the resulting Z3 story file in a compatible interpreter such as Windows Frotz.
Expect experimentation. ZILF is not Infocom’s original compiler, the source may need minor fixes, and a Z3 output file must be used with an interpreter that supports that Z-Machine version. Microsoft does not provide a complete dependency-installation guide or a cross-platform troubleshooting matrix.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What commercial developers should check
The MIT license makes commercial reuse of covered code possible, but it does not make a commercial Zork-branded product automatically safe. Before shipping, a developer should identify exactly which files are MIT-licensed, preserve the notices, and determine whether any included text or assets have separate rights.
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- Created in collaboration with movie trilogy co-writer and producer Bob Gale
- Features original movie cast members Christopher Lloyd ('Doc' Brown), Tom Wilson (Biff Tannen), Claudia Wells (Jennifer Parker), and in special cameo appearances, Michael J. Fox as McFlys of the past. And the future!
- Includes in-game access to exclusive content: a behind the scenes video featuring interviews with Bob Gale, Tom Wilson, members of the development team, and AJ LoCascio - the voice of young Marty McFly
- Your choices and actions change to story around you
- A classic Telltale game that lead to their breakout hits The Walking Dead, The Wolf Among Us, Game of Thrones, and Tales from the Borderlands
- Do not assume the Zork name, logos, or official-looking presentation are available.
- Do not reuse original packaging, manuals, maps, feelies, or artwork without separate permission.
- Review any original story text, characters, and other expressive material independently of the code license.
- Clearly distinguish a derivative project from an official Activision or Infocom release.
- Obtain qualified legal advice before selling a product that uses recognizable Zork branding or content.
Why the licensing matters for preservation
Making an archival source collection explicitly reusable helps researchers inspect how a landmark parser game was structured, lets students study legacy language and virtual-machine design, and gives developers a lawful basis for experiments, ports, tools, and educational forks. It also preserves more than a playable binary: comments, discarded material, and development files can reveal how interactive fiction was designed and produced.
The release is consequently both narrower and more useful than the phrase “Zork is free” suggests. It opens the covered source code while leaving the commercial presentation and brand ecosystem separate.
Bottom line
Yes: the source code for Zork I, Zork II, and Zork III is officially MIT-licensed. No: that license does not release every Zork asset or trademark. Buy the GOG anthology for the finished games; use the GitHub repositories, ZILF, and a Z-Machine interpreter to study and modify the historical code.
Quick Recap
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