Rapier

Sébastien Crozet and his company Dimforge released Rapier in 2020 as the successor to their earlier nphysics, which had turned out too slow. It has the usual parts of a physics engine — rigid bodies, colliders, joints, a broad phase and an impulse-based solver — but keeps its data in flat arrays rather than object trees.

Two things set it apart. There are ready-made JavaScript packages compiled to WebAssembly, and behind a feature flag the simulation is bit-for-bit deterministic across platforms, which makes it usable for lockstep and rollback netcode. In the Rust world it is the default choice, often through the Bevy plugin.