Components
Components are data attached to ECS entities. Source: src/components/.
Resources
Resources are singleton values stored globally in the Bevy World. Unlike components they are not attached to entities. Source: src/resources/.
Systems
Systems are functions that run on matching sets of entities every frame (or on a schedule). Source: src/systems/.
UI
The UI is implemented entirely with Bevy's native node-based UI system (no external UI crates). Source: src/ui/.