Microsoft Relicenses Infocom Classics: Zork I, Zork II, Zork III Now MIT-Licensed and Free for All

Microsoft has announced that the source code to the original Zork interactive fiction games, released by Infocom and today owned by Microsoft subsidiary Activision, is available under the permissive MIT license for the first time — allowing for redistribution, analysis, modification, and even derivative works.

"Today, we’re preserving a cornerstone of gaming history that is near and dear to our hearts. Together, Microsoft’s Open Source Programs Office (OSPO), Team Xbox, and Activision are making Zork I, Zork II, and Zork III available under the MIT License," Microsoft's Stacey Haffner and Scott Hanselman explain in the company's announcement. "Our goal is simple: to place historically important code in the hands of students, teachers, and developers so they can study it, learn from it, and, perhaps most importantly, play it."

The original Zork was developed by Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling and released for the Digital PDP-10 in 1977 — and the popularity of the text adventure, in which players typed written prompts to an in-game parser that would respond with pre-programmed room, item, and activity descriptions, would lead its creators to form Infocom in 1979 to commercialize the game.

Under Infocom, Zork — inspired by by Will Crowther's Colossal Cave Adventure, released in 1976 — would be expanded and split across three commercial titles released in 1980, 1981, and 1982. The games, and other Infocom titles, would sell well enough to raise the interest of Activision, which acquired the company in 1986 following Infocom's commercial misstep with a failed move into business software and expanded the Zork franchise to additional games and tie-in books. The birth of the graphical point-and-click adventure, which added interactive imagery and replaced the often all-too-picky text parser with a simple verb-and-noun mouse-driven interface, saw Infocom's fortunes shift, though, and as interactive fiction fell out of mainstream interest so too did Activision's desire to publish same.

With Activision itself having been acquired by Microsoft in 2023, Zork is enjoying something of a relaunch — with Microsoft officially relicensing an existing copy of the games' source code under the permissive MIT license. "Rather than creating new repositories," Haffner and Hanselman explain, "we're contributing directly to history. In collaboration with Jason Scott, the well-known digital archivist of Internet Archive fame, we have officially submitted upstream pull requests to the historical source repositories of Zork I, Zork II, and Zork III. Those pull requests add a clear MIT license and formally document the open-source grant."

The release means that anyone is free to study, redistribute, adapt, modify, and create derivatives of the games' source code, but only the source code. "This release focuses purely on the code itself," the pair say. "It does not include commercial packaging or marketing materials, and it does not grant rights to any trademarks or brands, which remain with their respective owners. All assets outside the scope of these titles' source code are intentionally excluded to preserve historical accuracy."

More information, including instructions on getting the games running on modern machines, can be found on the Microsoft blog; the source code is available in the Zork I, Zork II, and Zork III GitHub repositories under the MIT license.