// The engine that powers our games
Open Terrain Engine
An AI-native game engine. You direct an agent that writes the whole game in idiomatic, human-editable C#, introspects the running world as structured data, and verifies it through a deterministic, headless loop — and you can open and edit every line. It's the engine behind Empires of the Fallen World, and you can build on it too.
// What makes it different
AI-native, not AI-bolted-on
Agent-authored, human-editable C#
An LLM agent authors 100% of the game in idiomatic C# — the AI is the default author, not a wall. Open and edit any line, any time.
Deterministic by construction
A fixed-point simulation core is bit-identical across Linux and Windows, proven by a permanent cross-OS CI gate — the basis for lockstep, replays, and reliable AI verification.
Author → introspect → verify
The agent's loop: write C# → run headless → screenshot + state-dump → assert. Verify what you ship, not what you hope.
Model-agnostic MCP
A built-in, standard MCP server — drive it with any conformant LLM (Claude, ChatGPT, Gemini, or a local model). No vendor lock-in.
Genre-general
FPS, third-person, side-scroller/2.5D, top-down, and RTS as compositions of shared primitives — not separate products.
Native desktop
Linux + Windows, Vulkan via SDL3, .NET 10 / C# 14 — built for Steam.
// Licensing
Source-available, not open source
Open Terrain Engine is source-available / Fair Source under the Business Source License 1.1 — read it, learn from it, and build and ship your own games with it, including commercially. You just can't take the engine itself to market. Each version becomes Apache-2.0 on its change date. (Subject to final legal terms.)