Functional Programming GitHub Repositories (2026) · Open Source Tools

♞ lichess.org: the forever free, adless and open source chess server ♞

A fast, friendly, functional language.

Nix, the purely functional package manager

Hazel, a live functional programming environment with typed holes

Fastify 5 application boilerplate based on clean architecture, domain-driven design, CQRS, functional programming, vertical slice architecture for building production-grade applications 🚀

jank is the native Clojure dialect with seamless C++ interop.

A simple, lightweight, flexible, embeddable, portable and multi-paradigm dynamic programming language for developing applications, tools, and domain-specific languages

Kickstarter for iOS. Bring new ideas to life, anywhere.

A simple-to-use standalone Java library delivering boosted experience while working with YAML documents.

MimIR is my Intermediate Representation

Darklang main repo, including language, backend, and infra

Functional programming library for Go 1.24+, inspired by fp-ts. Uses generic type aliases for a clean, composable API. Provides Option, Either, Result, IO, IOResult, Reader, and ReaderIOResult monads, plus optics (Lens, Prism, Traversal) for immutable data manipulation. Supports Functor, Applicative, and Monad abstractions with do-notation-style

A universal language for business and technology

SQL DSL (Domain Specific Language) for Kotlin and Java. Supports rendering for MyBatis or Spring JDBC Templates

Kalandra is a functional, parallel, distributed programming language.

Ramda Adjunct is the most popular and most comprehensive set of functional utilities for use with Ramda, providing a variety of useful, well tested functions with excellent documentation.

A functional, Lisp-inspired language that compiles to PHP. Inspired by Clojure, Phel brings macros, persistent data structures, and expressive functional idioms to the PHP ecosystem.

🔮 A modern multi-paradigm compiled programming language for the JVM platform. website: https://ixionlang.ru/

DevTools and runtime environment for the Elm programming language

Code for Java upgrade workshop