A list of awesome beginners-friendly projects

If you are an open source project maintainer, add the label first-timers-only (or similar) to your project and list it here so people can find it.

.NET

• Shouldly (label: Jump-In) 
  Should testing for .net - the way Asserting Should be!

C

• Neovim (label: entry-level) 
  Vim-fork focused on extensibility and agility.

C++

• electron (label: help/beginner) 
  Build cross platform desktop apps with JavaScript, HTML, and CSS
• tensorflow (label: stat:contributions welcome) Computation using data flow graphs for scalable machine learning

Clojure

• Alda (label: low-hanging-fruit) 
  A music programming language for musicians. 

ClojureScript

• LightTable (label: beginner) 
  The Next Generation code editor! One of the top funded projects on KickStarter.

Dart

• webdev.dartlang.org (label: beginner) 
  A website for developers writing Dart web apps, including AngularDart apps.
• www.dartlang.org (label: beginner) 
  A website covering the Dart language and common libraries, for developers of Dart libraries, web apps, server-side code, and mobile (Flutter) apps.

Elixir

• Elixir (label: Level:Starter) 
  Elixir is a dynamic, functional language designed for building scalable and maintainable applications

Go

• Moby (label: exp/beginner) 
  Open-source application container engine
• Apex (label: contrib (easy)) 
  Build, Deploy, and Manage AWS Lambda functions with ease
• Hugo (label: exp/beginner) 
  A Fast and Flexible Static Site Generator built with love in GoLang
• CockroachDB (label: easy) 
  The Scalable, Survivable, Strongly-Consistent SQL Database
• Helm (label: starter) 
  The Kubernetes Package Manager

Java

• TEAMMATES (label: d.FirstTimers) 
  TEAMMATES is a free online tool for managing peer evaluations and other feedback paths of your students.
• elasticsearch (label: low hanging fruit) 
  Open Source, Distributed, RESTful Search Engine.
• JabRef (label: beginner) 
  Desktop application moving from SWING to JavaFX. Focus on code quality: Usage of code quality tools such as CodeCov and Codacy. Each Pull Request is reviewed by two developers to provide high-quality feedback and to ensure high quality of new contributions.
• Wikimedia Commons Android App (label: beginner friendly) 
  Allows users to upload pictures from their Android phone/tablet to Wikimedia Commons.

JavaScript

• annyang (label: first-timers-only) 
  A popular Speech Recognition library used to communicate with everything from websites to smart mirrors to flying drones.
• Clementine.js Boilerplate (label: beginner) 
  The elegant and lightweight full stack JavaScript boilerplate.
• PouchDB (label: first time only) 
  PouchDB is a pocket-sized database.
• Leaflet (label: easy fix) 
  JavaScript library for mobile-friendly interactive maps.
• angular-formly (label: first-timers-only) 
  JavaScript powered forms for AngularJS.
• Dragula (label: first-timers-only) 
  Drag and drop so simple it hurts.
• UI.Layout directive (Angular UI) (label: first-timers-only) 
  Angular directive that allows you to split!
• history (label: good-for-beginner) 
  A minimal, functional history library for JavaScript.
• TodoMVC (label: first time contributor) 
  Helping you select an MV* framework by implementing Todo in lots of Javascript apps.
• Adobe Brackets (label: starter bug) 
  An open source code editor for the web, written in JavaScript, HTML and CSS.
• AVA (label: good for beginner) 
  Futuristic test runner.
• Kinto.js (label: easy-pick) 
  An offline-first JavaScript client leveraging the Kinto API for remote data synchronization.
• ESLint (label: beginner) 
  A fully pluggable tool for identifying and reporting on patterns in JavaScript.
• Webpack (label: D0: My First Commit (Contrib. Difficulty)) 
  A bundler for javascript and friends.
• Tessel 2 CLI (label: contribution-starter) 
  Command line interface to Tessel 2.
• Ember.js (label: Good for New Contributors) 
  A JavaScript framework for creating ambitious web applications.
• Ember.js Data (label: Good for New Contributors) 
  A data persistence library for Ember.js.
• FreeCodeCamp (label: first-timers-only) 
  Open source codebase and curriculum. Learn to code and help nonprofits.
• Ghost (label: beginner) 
  Just a blogging platform
• eslint-plugin-unicorn (label: good for beginner) 
  Awesome ESLint rules.
• Hyper (label: Good for beginners) 
  JS/HTML/CSS Terminal
• pdf.js (label: 5-good-beginner-bug) 
  PDF Reader in JavaScript
• Moment.js (label: Up-For-Grabs) 
  A lightweight JavaScript date library for parsing, validating, manipulating, and formatting dates.
• serverless (label: help-wanted-easy) 
  The Serverless Framework
• Hoodie Camp (label: first-timers-only) 
  Hoodie Camp is a space for new and existing contributors.
• React server (label: good-first-contribution) 
  React framework with server render for blazing fast page load and seamless transitions between pages in the browser.
• Yarn (label: good-first-contribution) 
  Fast, reliable, and secure dependency management.
• pixi.js (label: Difficulty: Easy) 
  A 2D JavaScript Renderer
• Next.js (label: Good for beginners) 
  A minimalistic framework for universal server-rendered React applications
• keystonejs (label: good first task) 
  The open source framework for developing database-driven websites, applications and APIs in Node.js. Built on Express and MongoDB.
• Semantic-UI-React (label: good first contribution) 
  The official React integration for Semantic UI.
• Botpress (label: for-new-contributors) 
  The only sane way to build great bots.
• Atom (label: beginner) 
  The hackable text editor
• cdnjs (label: BEGINNER) 
  The best FOSS web front-end resource CDN
• Video.js (label: first-timers-only) 
  The player framework
• stryker (label: beginner friendly) 
  The JavaScript mutation testing framework

Julia

• Julia Language: Intro Issues (label: intro issue) 
  "Move like Python, Run like C" - A fresh approach to technical computing!
• Julia Language: Up for Grabs (label: up for grabs ) 
  "Move like Python, Run like C" - A fresh approach to technical computing!

PHP

• phpMyAdmin (label: newbie) 
  Admin interface for MySQL written in PHP.
• Deployer (label: good for beginner) 
  A deployment tool written in PHP with support for popular frameworks out of the box.
• Piwik (label: Easy Pick) 
  Piwik is the leading Free/Libre open analytics platform.
• OrgManager (label: beginners-only) 
  Supercharge your GitHub organizations!

Python

• catapult (label: Good First Bug) 
  Catapult home for performance tools.
• Python Babel (label: difficulty/low) 
  The Python Internationalization Library.
• Kinto (label: easy-pick) 
  A lightweight JSON storage service with synchronisation and sharing abilities.
• BorgBackup (label: easy) 
  Deduplicating backup program with compression and authenticated encryption.
• pylearn2 (label: For beginners) 
  A Machine Learning library based on Theano.
• scrapy (label: easy) 
  A fast high-level web crawling & scraping framework for Python.
• mitmproxy (label: good first contribution) 
  An interactive TLS-capable intercepting HTTP proxy for penetration testers and software developers
• Mailpile (label: low hanging fruit) 
  A free & open modern, fast email client with user-friendly encryption and privacy features
• coala (label: difficulty/newcomer) 
  A unified command-line interface for linting and fixing all your code, regardless of the programming languages you use.
• jarvis (label: difficulty/newcomer) 
  A personal assistant for Linux based on Command line Interface.
• qutebrowser (label: easy) 
  A keyboard-driven, vim-like browser based on PyQt5.
• Pybee/voc (label: first-timers-only) 
  A transpiler that converts Python code into Java bytecode.
• Pybee/batavia (label: first-timers-only) 
  A Javascript implementation of the Python virtual machine.
• JARVIS-on-Messenger (label: Low-Hanging Fruit) 
   A community-driven python bot that aims to be as simple as possible to serve humans with their everyday tasks http://m.me/J.A.R.V.I.S.on.Messenger
• Gratipay (label: Low-hanging Fruit) 
  Helping companies and others pay for open source.
• Pytest (label: easy) 
  The pytest framework makes it easy to write small tests, yet scales to support complex functional testing.
• Fabric (label: Low-hanging fruit) 
  Pythonic remote execution and deployment.

Ruby

• JRuby (label: beginner) 
  An implementation of Ruby on the Java Virtual Machine.
• puppet-mcollective (label: beginner friendly) 
  MCollective Server and Client Puppet Module.
• Sinatra (label: your-first-pr) 
  Classy web-development dressed in a DSL.
• Goby (label: beginner) 
  Framework for developing text-RPGs.
• Hanami (label: easy) 
  A modern framework for Ruby.
• operationcode (label: beginner friendly) 
  An open source community dedicated to getting military veterans coding._
• chef (label: Type: Jump In) 
  A systems integration framework, built to bring the benefits of configuration management to your entire infrastructure
• ohai (label: Type: Jump In) 
  Ohai profiles your system and emits JSON
• PublicLab.org (label: first-timers-only) 
  An open source publishing platform for environmental projects. Check out new contributors welcome page.

Rust

• Servo (label: E-easy) 
  A browser engine designed for applications including embedded use.
• Rust-Clippy (label: E-easy) 
  A bunch of lints to catch common mistakes and improve Rust code
• Rustfmt (label: easy) 
  A tool for formatting Rust code according to style guidelines.
• Iron (label: easy) 
  An extensible, concurrent web framework for Rust

Scala

• Twitter Util (label: Starter) 
  Wonderful reusable code from Twitter
• playframework (label: newbie) The High Velocity Web Framework

TypeScript

• TypeScript (label: Effort: Easy) TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
• Visual Studio Code (label: beginner) a new type of tool that combines the simplicity of a code editor with what developers need for their core edit-build-debug cycle.