Machina.js is a TypeScript-first finite state machine library that provides both single-client and multi-client FSM implementations. It features hierarchical state machines with event bubbling, deferred input processing, lifecycle hooks, and a built-in event system. The library includes static analysis tools for detecting unreachable states and transition loops, testing utilities with custom matchers, React integration hooks, and an ESLint plugin for FSM validation. Built as a monorepo with pnpm and turbo, it emphasizes type safety and compile-time validation of state configurations.