Figma is really pretty revolutionary as far as web apps go, both from the design side (collaborative, beautiful, and easy to use) and from the dev side (realtime multiplayer, fast stateful graphics with undo/redo, incredibly complex UI, built in a combination of WebGL, WASM, and Workers).

For a while before it, Sketch was the dominant UX/UI tool, but then Figma came outta nowhere and surprised the world by showing what could be accomplished with a web app, using a freemium model, developed by a previously unknown company.

As far as unicorns go, I can't think of many startups that have delivered similarly amazing value (maybe Cloudflare and Vercel?), and certainly none in the design space. Like Canva and Draw.io etc. are alright, but Figma is really technologically impressive (and beautiful, and usable!).

If you ever see a complex UI that you enjoy using... chances are very high Figma was used for some part of it.