BRUTAL, the C# framework behind RimWorld's new engine, goes open source

Ahwoo and RocketWerkz have released BRUTAL as open source. Announced from Auckland on 15 October, it is a C# framework you can use to build a game directly, or as the foundation for your own engine. It is free to use, including in commercial games, with no royalties and no share of your revenue.

BRUTAL is not a general-purpose engine, and it isn't trying to be one. At its core is an interop layer that connects modern C# and .NET to native APIs and C/C++ libraries, including Vulkan. Around that sit libraries for maths, memory management, job scheduling, logging and localisation, written to cut allocations and overhead. Ahwoo says it grew from a small set of libraries over four years, with a deliberate focus on low-level features.

It is already in production. Ludeon Studios used it to build Waylith, the new engine for RimWorld, and reported two to four times better performance in its tests. RocketWerkz builds Kitten Space Agency on it, plus Art of the Rail and Torpedia. In total it powers six projects across three studios, and Kerbal Space Program creator Felipe Falanghe is using it for his next game.

The name is a fair warning. Ahwoo's head of engineering, Rian Drake, says there are "no guardrails": you build, and maintain, the systems your game needs.

Why it matters: if you want to own your tech without starting from zero, BRUTAL gives you foundations that shipping teams already rely on. It is aimed at experienced programmers, so expect to write the engine parts yourself.