All in one

• The Cyber Swiss Army Knife - A web app for encryption, encoding, compression and data analysis - Try it!

ASCII Art

• aalib.js - ASCII art library in JavaScript - Try it!
• ASCII-Artist - A pure html/javascript ASCII Art Generator
• AsciiMorph - Library to animate between two ascii images - Try it!
• Dom Animator - A nifty javascript library to run animations, hidden in comment nodes, within the dom - Try it!
• imgToAscii - A JavaScript implementation of a image to Ascii code - Try it!
• Lettercrap - A Javascript library that generates dynamic ascii art on the web Try it!

Beautifier / Minifier

• csso - CSS minifier with structural optimizations - Try it!
• html-minifier - Javascript-based HTML compressor/minifier - Try it!
• JSON Lint - JSON parser and validator with a CLI - Try it!
• UglifyJS - JavaScript parser / mangler / compressor / beautifier toolkit Try it!
• js-beautify - Beautifier for javascript - Try it!

CMS

• CMS.js - Client-Side JavaScript Site Generator - Try it!
• coisas - a client-side CMS for editing GitHub Markdown (and other) files - Try it!

Converter

• reMarked.js - client-side HTML > markdown - Try it!

Editor

• angular-cron-gen - A basic way to for users to graphically build a cron expression using Angular - Try it!
• cleditor - a lightweight jQuerified HTML editor Try it!
• draw.io - A JavaScript, client-side editor for general diagramming and whiteboarding - Try it!
• TinyMCE - JavaScript library for rich text editing. Available for React, Vue and Angular - Try it!
• ZenPen - A minimalist writing zone Try it!

Langages

Golang

• Go Template Preview - Quickly test and visualize your Go templates live - Try it!
• curl-to-go - Convert curl commands to Go code in your browser - Try it!
• json-to-go - Translates JSON into a Go type in your browser instantly - Try it!

Node.js

• broserify - browser-side require() the node.js way - Try it!

Python

• Brython - Try it!
• Pyodide - A Python distribution for the browser and Node.js based on WebAssembly.
• PyScript - A framework that allows users to create rich Python applications in the browser using HTML's interface and the power of Pyodide, WASM, and modern web technologies - Try it!

Low level

Python

• Serial Terminal - An Open-Source Web-based Serial Terminal - Try it!
• espwebtool - A web app to flash your ESP32 or ESP8266 through your browser. Open-Source, free, and easy to use - Try it!

Multimedia

Image

• angular-image-crop - A better way to crop images client-side using AngularJS - Try it!
• compress.js - A simple JavaScript based client-side image compression algorithm - Try it!
• Generative Artistry
• holder - Client-side image placeholders - Try it!
• Intense Images - A simple library to view large images up close using simple mouse interaction, and the full screen - Try it! - A website for self coding generative art tutorials - Try it!
• MarvinJ - Javascript Image Processing Framework based on Marvin Framework Try it!
• NSFW JS - NSFW detection on the client-side via TensorFlow.js Try i!
• webp2jpg-online - Image conversion and image stitching, pure front-end implementation, fast speed, privacy protection, and offline use - Try it!

Video

• videoinput.js - video-input field to make video recording easy via client-side JS - Try it!

Paste Service

Video

• 0bin - Client side encrypted pastebin - Try it!
• NoPaste - Client-side paste service - Try it!
• paste - A no-datastore, client-side paste service - Try it!

PDF

Video

• html2pdf.js - Client-side HTML-to-PDF rendering using pure JS. - Try it!
• jsPDF - Client-side JavaScript PDF generation for everyone Try it!
• pdf.js - PDF Reader in JavaScript - Try it!
• WASM-PDF - Generate PDF files with JavaScript and WASM (WebAssembly) - Try it!

Peer-to-peer

Video

• torrent-client - Torrent Web client - Try it!
• Chitchatter - A peer-to-peer chat app that is serverless, decentralized, and ephemeral - Try it!
• FilePizza - 🍕 Peer-to-peer file transfers in your browser - Try it!
• Magnet Placer - 🎥 A place for streaming torrents directly from your browser - Try it!
• PeerTube - ActivityPub-federated video streaming platform using P2P directly in your web browser - Try it!
• TorrenParts - 📑 A website to inspect and edit what's in your Torrent file or Magnet link - Try it!
• WebTorrent - ⚡️ Streaming torrent client for the web - Try it!

QRCode

Video

• EasyQRCodeJS - A feature-rich cross-browser pure JavaScript QRCode generation library - Try it!
• jsqrcode - Javascript QRCode scanner - Try it!
• qrcode - A simple, small, progressive web app that accesses the user's camera and looks for QR Codes - Try it!

Security

Video

• Argon2 in browser - Argon2 password-hashing library compiled for browser runtime - Try it!
• de4js - JavaScript Deobfuscator and Unpacker - Try it!
• ducksify - BadUSB Script Converter - Try it!
• hat.sh - Encrypt and Decrypt files securely in your browser - Try it!
• javascript-deobfuscator - General purpose JavaScript deobfuscator - Try it!
• javascript-obfuscator - A powerful obfuscator for JavaScript and Node.js - Try it!
• jsfuck - Write any JavaScript with 6 Characters: []()!+ - Try it!
• Lufi - Lufi means Let's Upload that FIle. It's a E2E encrypted file sharing software - Try it!
• password-generator - Web Password Generator - Try it!

Template Engine

Video

• json2html - Json2html is a lightning fast client side javascript HTML templating library with wrappers for both jQuery and Node.js - Try it!

WebAssambly

Video

• WABT - The WebAssembly Binary Toolkit - Try it!