@tracked is a decorator for Preact that makes working with state values no different than properties on your component instance.
It's one 300 byte function that creates a getter/setter alias into state/setState() for a given key, with an optional initial value. The "magic" here is simply that it works as a property decorator rather than a function, so it appears to integrate directly into the language.
tracked has no dependencies and works with any component implementation that uses this.state and this.setState().