CSS Scan - Instantly check or copy computed CSS from any element for only ~95$
Blazor - An experimental web UI framework using C#/Razor and HTML, running in the browser via WebAssembly
Hoverify - All-in-one browser extension to improve your web dev experience.
Angular.io - Angular is a JavaScript web framework for creating single-page web applications. The code is free to use and available as open source. It is further maintained and heavily used by Google and by lots of other developers around the world.
CSS Grab n' Go Editor - Visual editor for learning and quick CSS mocking
React - A JavaScript library for building user interfaces