An in-browser animation editor was posted to HN by @AshleyGullen. It's snappy and obvious that it's handcrafted JS, à la Photopea. Super obvious.
An HNer asks about what UI framework it's using. The answer is "none", and the founder replies, saying so: "all written from the ground up in house". This is beyond the comprehension of another user who chimes in. @AshleyGullen has to step in and reiterate that they wrote it all.