Box3D

Box3D is a 3D physics engine for games — rigid-body dynamics, collision detection, and constraint solving — written by Erin Catto, the author of the widely used 2D engine Box2D. It is the 3D successor to Box2D, carrying the same design lineage into three dimensions. First tagged release v0.1.0 landed June 2026, so it is early and still stabilising (pull requests are disabled pending stabilisation), but it inherits years of Box2D solver experience box3d.

Box3D is a middleware component, not a game engine: it simulates physics and hands results back to whatever renders and runs the game. That is the same layer engines in this wiki embed rather than replace — Godot ships the Jolt physics backend, and Phaser/Torque2D embed Box2D (Box3D’s 2D sibling) for their 2D physics. So Box3D sits one level below the engines here: a swappable physics core an engine or a hand-rolled game loop can build on.

Technology

• Language: core in C17; the samples require C++20.
• Architecture: data-oriented design with extensive multithreading and SIMD, tuned for “large piles of bodies” — many interacting rigid bodies at once.
• Solver: a “Soft Step” constraint solver (the robustness pitch), with island-based sleep (idle groups of bodies stop consuming CPU) and cross-platform determinism (the same inputs produce the same simulation on every platform — the property multiplayer and replay depend on).
• Collision: continuous collision detection, convex hulls, capsules, spheres, meshes, height fields, and raycasting.
• Joints: revolute, prismatic, motor, and weld, with joint limits and motors.
• Tooling: recording/replay; samples use the Sokol graphics library for rendering and Dear ImGui for their UI.

Positioning

• License: MIT — permissive, matching the open pole this wiki tracks (godot-engine, o3de, flame-engine, carbon-engine).
• Platforms: Windows, Linux, macOS.
• Maturity: v0.1.0 (June 2026); new codebase, established author.

Determinism plus MIT licensing makes Box3D a candidate physics core for the deterministic-sim genres this wiki already tracks — the massive-battle RTS engines (spring-rts, openage) and MMO-scale sims (Carbon, whose Destiny component is CCP’s in-house physics+pathfinding layer) all lean on deterministic physics for the same reasons.