External Tools - crucial.tools

JSFiddle Popular JavaScript sandbox and testing web tool that also allows you to mock up an entire page (HTML, CSS, etc.).
Playcode A good, complete silo system, which lets you test client-side web code in a sandbox environment.
W3C Markup Validator Online tool to verify or correct your web page's markup (HTML).
RegEx Library A great place for all things related to regular expressions, including a multi-platform test environment and a very helpful cheatsheet.
Font Awesome A huge range of free icons collected together in a single library, so you can avoid excess images, and scale icons smoothly.
WAVE ADA Compliance Checker Web tool that checks your web page's WCAG compliance, and helps improve the experience for visitors who have disabilities.
Python Online Compiler A slick online REPL (programming environment) for the Python programming language, that let's you explore and test in a sandbox environment.
Flexy Boxes Online sandbox for learning and fine-tuning the Flexbox HTML responsive layout system.
Regular Expressions 101 Regular expression sandbox and online tester that simulates several different RegEx frameworks.
SEOptimer Search Engine Optimization audit and reporting tool that helps identify SEO gaps in your website.
Mozilla Observatory Mozilla's online tool that performs a security audit on your website, and offers security suggestions.

University of the People Non-profit organization that offers very low-cost degree programs in business admin, education, computer science, and health science.
Internet Archive A vast library of public domain audio, video, software, and video games, and historical snapshots of web pages.
Alison Free Courses Another great resource for free online courses (and also some diplomas), spanning a variety of topics.
edX Online Courses Online education platform offering free courses from some of America's top universities on a diverse number of topics.
Mozilla Development Network Documentation A broad range of online web development tools, documentation, and training resources, courtesy of Mozilla.
Wikipedia English language version of the massive, free online encyclopedia that's community built and maintaned.
Open Culture Free Online Courses A very large and diverse selection of free courses from some of the world's top universities.
Stack Overflow The go-to online knowledge-sharing resource for software and web developers all over the world.
Khan Academy Non-profit organization that hosts a huge array of free online courses covering many different topics.
W3Schools A great selection of simple and easy-to-follow tutorials on using various web development languages and technologies.
Udemy Free Courses An assortment of online courses currently being offered free by Udemy, a popular online learning platform.

Freerange Large library of good quality, royalty free, stock images that are also free to download.
Audio Joiner Online tool that allows you to splice multiple audio files together into a single file.
Audacity An open source, feature-rich, audio editing desktop application that has become an essential tool to millions.
Vectr A feature-rich, online tool for creating vector graphics (there is also a desktop version available).
Favicon.io Online tool that allows you to convert an image into different sized Windows icon (.ico) files.
Inkscape A very slick, easy-to-use, and free to use, desktop application for creating vector graphics.
Audioalter Audio converter that turns a standard stereo audio file into an enhanced 8D audio file.
CDex A great, free, audio file convertor and CD ripper that supports many different file formats.
VLC Media Player Another piece of stand-out software, VLC is the leading open source video and audio playback tool on many operating systems.

LibreOffice An open source desktop software suite that featues word processing, spreadsheet editing, and other office productivity tools.
Ubuntu Operating System An establish distro (version) of the Linux operating system that is beginner-friendly and feature-rich.
Discord An intuitive and feature-rich group and collaboration platform that's moved far beyond its gamer roots.
Google Docs Google's very popular online office suite (word processor, spreadsheet editor, etc.).
Bit Warden A very nice open source password manager that's secure, easy-to-use, and can be accessed across multiple platforms.
Musescore A free desktop application that allows you to write and transpose sheet music.
Online2PDF Online tool that allows you to convert documents of a variety of formats into PDF files.
DuckDuckGo A privacy-respecting search engine that provides pertinent results, and which offers various consumer-friendly add-on products.
Standard Notes Easy-to-use, secure open-source repository for all your digital data, accessible via apps on basically every platform.