The Dark Mod is a free and open-source first-person stealth game inspired by Looking Glass Studios’ Thief series. Set in a gothic steampunk world of gaslit streets, cathedral vaults and inventor’s mansions, it casts you as an agile thief who must slip past guards, traps and creatures using shadows, sound and a carefully chosen toolkit rather than brute force. It began in 2009 as a total-conversion mod for Doom 3 and became fully standalone in 2013, running on the open-sourced id Tech 4 engine.

The Dark Mod is less a single campaign than a platform: it ships the engine, assets and a purpose-built editor as a toolkit for the community, which has produced more than 190 fan-made missions and several multi-mission campaigns. The latest release is 2.14 (March 2026).

Key Features

• Light-based stealth — a light gem shows exactly how visible you are; staying in shadow is the core survival mechanic.
• Thief-style toolkit — blackjack, water arrows to douse torches, holy water, flashbombs, mines, rope arrows and more.
• Mission platform — 190+ community missions and campaigns, downloadable from within the game.
• DarkRadiant editor — a dedicated open-source level editor for Windows and Linux so you can build and share your own missions.
• id Tech 4 engine — the open-sourced Doom 3 engine, with native 64-bit builds and modern renderer improvements.
• Reactive AI & physics — guards respond to sight, sound and light; bodies, traps and creatures behave dynamically.
• Standalone & free — no Doom 3 installation required since version 2.0; free to download, play and modify.
• Cross-platform — native builds for Windows, Linux and macOS.

Why Use The Dark Mod?

It is the closest thing to a modern, actively maintained Thief-style stealth game that is completely free and open source. Because the source, assets and editor are all released, it doubles as a modding and level-design playground, and the steady stream of fan missions means there is always new content. It also runs well on modest hardware and is fully supported on Linux.

Use Cases

• Playing atmospheric first-person stealth missions without paying for a commercial title.
• Creating and sharing your own stealth levels with the DarkRadiant editor.
• Studying or modding a real id Tech 4 codebase for game-development learning.
• Running classic stealth gameplay natively on Linux, Windows or macOS.

Platform

Windows · Linux · macOS

Licence

The game engine’s source code is free software, released under the GNU GPL v3 (or later) together with a revised BSD licence. Non-software components (maps, textures, models, audio) are licensed under Creative Commons BY-NC-SA 3.0, and individual fan missions remain the property of their authors. See the LICENSE.txt.

Similar open-source games

• Xonotic — another free, open-source first-person game for Windows, Linux and macOS

Website

thedarkmod.com