XState is a production-grade TypeScript library for creating, interpreting, and executing finite state machines and statecharts, based on the SCXML standard and the actor model. The repository is a monorepo (pnpm workspaces) containing the core `xstate` package, the lighter `@xstate/store` for event-sourced state management, and framework-specific bindings for React, Vue, Svelte, Solid, Preact, and Angular. It also includes `xstate-inspect` for debugging, `xstate-immer` for Immer integration, a graph analysis module for model-based testing, and many example applications and templates. The core engine provides `createMachine`, `createActor`, `setup()` for type-safe machine definitions, built-in actions (assign, sendTo, raise, etc.), guard combinators, and actor logic factories (`fromPromise`, `fromCallback`, `fromObservable`). The store sub-package offers atoms, source atoms, and composable extensions like persist and undo/redo. The codebase demonstrates high craftsmanship with extensive TypeScript type inference, well-encapsulated modules, and comprehensive test coverage. It is actively maintained with continuous CI/CD and version management via changesets.
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.
maxapi is an async Python SDK and bot framework for the MAX messenger platform. It provides a high-level client (`Bot`) for all MAX Bot API endpoints, an event-driven dispatcher with router hierarchy (`Dispatcher`/`Router`), composable filters (magic filter `F`, `Command`, `StateFilter`, etc.), middleware chains, a finite state machine (FSM) with multiple backends (memory, Redis), and webhook integrations for aiohttp, FastAPI, and Litestar. The library is heavily inspired by aiogram but adapted to MAX API specifics such as attachment types, callback payloads, and deep linking. It includes extensive utility code for formatting (HTML/Markdown), inline keyboard building, VCF parsing, and time helpers. The codebase is well-structured with Pydantic v2 models for all API entities, rigorous retry logic, and a comprehensive test suite covering unit, integration, and webhook scenarios. While not a standalone application, it serves as a foundational component for building production-ready MAX bots.
libfsm is a C library and toolchain for constructing, manipulating, and compiling finite state machines (FSMs) from regular expressions. It supports multiple regex dialects (PCRE, glob, SQL LIKE, literal, native) and compiles them into deterministic finite automata (DFAs) that guarantee linear-time matching. The library provides a rich set of FSM operations: determinisation, minimisation, union, intersection, complement, reversal, trimming, and more. It also includes a lexer generator (lx) that produces C lexers from specification files, and a pattern matcher builder (rx) that merges many patterns into a single DFA with conflict detection. The architecture is modular: an abstract data type (ADT) layer provides reusable data structures (sets, hash tables, priority queues, edge sets, interned state sets); the libfsm core implements FSM algorithms; libre handles regex parsing and AST analysis; and multiple code generation backends emit C, Rust, Go, LLVM IR, x86 assembly, awk, shell, JSON, and a custom VM bytecode. The build system uses BSD make (bmake) and the project is extensively tested with unit tests, property-based fuzzing (theft), and a cross-implementation test runner (retest) that compiles and runs generated code via dlopen. Key entry points include the fsm CLI tool for interactive FSM operations, the re CLI for regex compilation and code generation, the lx CLI for lexer generation, and the rx CLI for building pattern matchers. The library is designed for embedding in other applications, with allocator hooks and a clean public API. It is particularly suited for high-performance pattern matching, protocol parsing, and any domain requiring deterministic automata with guaranteed worst-case performance.
Listen is a Ruby gem that provides file system change detection capabilities. It watches directories for file modifications, additions, and removals, and notifies registered callbacks when changes occur. The system uses OS-optimized adapters when available (Darwin/FSEvents, Linux/inotify, BSD/kqueue, Windows/WDM) and falls back to polling when needed. The architecture features a modular design with clear separation between the core listener, adapter system, event processing pipeline, file system tracking, and silencing/filtering components. Key entry points include the Listen.to() method and the bin/listen executable.