Shouldly(label: Jump-In) Should testing for .net - the way Asserting Should be!
MvvmCross(label: first-timers-only) The .NET MVVM framework for cross-platform solutions, including Xamarin.iOS, Xamarin.Android, Windows and Mac.
C
Neovim(label: good first issue) Vim-fork focused on extensibility and agility.
C++
electron(label: good first issue) Build cross platform desktop apps with JavaScript, HTML, and CSS
Godot Engine(label: junior job) 2D and 3D cross-platform game engine. Also has C# and Python code.
tensorflow(label: stat:contributions welcome) Computation using data flow graphs for scalable machine learning
projectM(label: good first issue) A music visualizer library using OpenGL and GLSL. Has applications using Qt5, SDL, emscripten, iTunes, Kodi.
Roc(label: help wanted) A toolkit for real-time audio streaming over the network.
Clojure
Alda(label: low-hanging-fruit) A music programming language for musicians. 🎶
ClojureScript
LightTable(label: good first issue) The Next Generation code editor! One of the top funded projects on KickStarter.
Dart
dart.dev(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
Ecto(label: Level:Starter) Ecto is a database wrapper and language integrated query for Elixir
Kubernetes(label: good first issue) Production-Grade Container Scheduling and Management System
TiDB(label: for new contributors) A distributed scalable Hybrid Transactional and Analytical Processing (HTAP) database
Java
Strongbox(label: good first issue) Strongbox is an artifact repository manager written in Java.
TEAMMATES(label: d.FirstTimers) TEAMMATES is a free online tool for managing peer evaluations and other feedback paths of your students.
elasticsearch(label: good first issue) Open Source, Distributed, RESTful Search Engine.
JabRef(label: good first issue) 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.
XWiki(label: Onboarding) XWiki is a free wiki software platform written in Java with a design emphasis on extensibility. Beginners should follow the onboarding wiki.
zerocode(label: good first issue) API Automation without coding, easy JSON response assertions, Testing REST, SOAP, Kafka and Java/DB APIs, CI/Jenkins Friendly.
JavaScript
name-suggestion-index(label: good first issue) Canonical common brand names for OpenStreetMap
iD(label: good first issue) The easy-to-use OpenStreetMap editor in JavaScript.
missioncontrol(label: first-timers-only) Mission Control is a free and open marketplace connecting autonomous vehicles (e.g., drones) with users looking for services such as package deliveries.
missions(label: first-timers-only) Missions is a mobile web app connecting DAV users looking to ship packages with autonomous drones looking for work in an open and free marketplace.
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: good first issue) JavaScript library for mobile-friendly interactive maps.
Dragula(label: first-timers-only) Drag and drop so simple it hurts.
Hyper(label: good first issue) 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(label: good first issue) A declarative, efficient, and flexible JavaScript library for building user interfaces.
React Native(label: Good first issue) A framework for building native apps with React.
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 issue) Fast, reliable, and secure dependency management.
pixi.js(label: Difficulty: Easy) A 2D JavaScript Renderer
Next.js(label: good first issue) 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 issue) The official React integration for Semantic UI.
electron(label: good first issue) Build cross platform desktop apps with JavaScript, HTML, and CSS
Botpress(label: good first issue) The only sane way to build great bots.
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
Kap(label: good first issue) An open-source screen recorder built with web technology
Reddit Enhancement Suite(label: help wanted) A browser extension to enhance the Reddit browsing experience.
Brave Browser(label: good first bug) Desktop browser for macOS, Windows, and Linux.
Fastify(label: good first issue) Fast and low overhead web framework, for Node.js.
Node.js core(label: good first issue) JavaScript runtime built on Chrome's V8 JavaScript engine
Jest(label: good first issue) A complete and easy to set up JavaScript testing solution.
Mattermost(label: Up For Grabs, Difficulty:1/Easy, Tech/JavaScript) Open source Slack-alternative in Golang and React
p5.js(label: good first issue) p5.js is a client-side JS platform that empowers artists, designers, students, and anyone to learn to code and express themselves creatively on the web.
squirrelly(label: good first issue) Squirrelly is a lightweight template engine that supports helpers, filters, partials, and more.
NativeScript(label: good first issue) NativeScript is an open source framework for building truly native mobile apps with JavaScript. Use web skills, like Angular and Vue.js, FlexBox and CSS, and get native UI and performance on iOS and Android.
Gatsby.js(label: good first issue) Build blazing fast, modern apps and websites with React.
Vue.js(label: good first issue) The Progressive JavaScript Framework.
md-page(label: good first issue) Create a webpage with just markdown.
Check It Out(label: good first issue) Check It Out is an ncurses-like CLI to let the user interactively navigate and select a git branch to check out.
nuclear(label: good first issue) Multiplatform music player that streams from free sources.
material-ui(label: good first issue) React components for faster and easier web development. Build your own design system, or start with Material Design.
Julia
Julia Language: Help wanted(label: help wanted) "Move like Python, Run like C" - A fresh approach to technical computing!
Julia Language: Good first issue(label: good first issue ) "Move like Python, Run like C" - A fresh approach to technical computing!
Kotlin
Atrium(label: good first issue) Multiplatform assertion library for Kotlin
Hexagon(label: help wanted) A microservices toolkit written in Kotlin
Perl
Ravada(label: good first issue) Remote Virtual Desktops Manager.
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.
Matomo(label: help wanted) Matomo is the leading Free/Libre open analytics platform.
OrgManager(label: beginners-only) Supercharge your GitHub organizations!
PHP Censor(label: good-for-beginner) Open source self-hosted continuous integration server for PHP projects.
Drupal(label: N/A, link to external website) Leading open-source CMS for ambitious digital experiences that reach your audience across multiple channels.
Python
catapult(label: Good First Bug) Catapult home for performance tools.
CiviWiki(Good First Issue) Building a Better Democracy for the Internet Age
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.
scrapy(label: good first issue) 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.
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.
Pytest(label: status: 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.
Jupyter notebook(label: good first issue) Jupyter interactive notebook.
Concept to Clinic(label: good first issue) Aims to develop an end-to-end application for lung cancer detection that connects the predictive power of machine learning with functional software tested against errors and a clean user interface focused on clinical use.
Zulip(label: good first issue) Powerful open source group chat.
cookiecutter(label: low-hanging-fruit) A command-line utility that creates projects from cookiecutters (project templates). E.g. Python package projects, jQuery plugin projects.
django cookiecutter(label: django hacktober special) An implementation of Python for backend web development.
wemake-python-stylegide(label: level:starter) The strictest and most opinionated python linter ever!
Ansible(label:easyfix) A simple IT automation platform
opsdroid(label: good first issue) An open source chat-ops bot framework.
pandas(label: good first issue) Flexible and powerful data analysis / manipulation library for Python, providing labeled data structures similar to R data.frame objects, statistical functions, and much more
VPN@Home(label: good first issue) 1-click OpenVPN deployment and management dashboard.
SaltStack(label: Low-Hanging Fruit) Software to automate the management and configuration of any infrastructure or application at scale.
mygpo(label: starter-issue) The webservice for gpodder.net, a libre web service that allows users to manage their podcast subscriptions and discover new content.
osem(label: good first issue) Open Source Event Manager. An event management tool tailored to Free and Open Source Software conferences See "How to contribute to osem"
bolt(label: Beginner Friendly) Bolt is a Ruby command-line tool for executing commands, scripts, and tasks on remote systems using SSH and WinRM.
Rust
Servo(label: E-easy) A browser engine designed for applications including embedded use.
Rust-Clippy(label: good first issue) A bunch of lints to catch common mistakes and improve Rust code
Rustfmt(label: good-first-issue) A tool for formatting Rust code according to style guidelines.
Iron(label: easy) An extensible, concurrent web framework for Rust
TiKV(label: D: Easy) A distributed transactional key-value database
nushell(label: good first issue) A modern shell for the GitHub era written in Rust.
Hyper(label: E-easy) A fast, safe and correct low-level HTTP library for Rust.
Scala
Twitter Util(label: good first issue) Wonderful reusable code from Twitter
playframework(label: good first issue) The High Velocity Web Framework
TypeScript
TypeScript(label: good first issue) A superset of JavaScript that compiles to clean JavaScript output.
Visual Studio Code(label: good first issue) A new type of tool that combines the simplicity of a code editor with what developers need for their core edit-build-debug cycle.
tslint-eslint-rules(label: nice first contribution) ESLint rules for TSLint.