alt Hacker NewsBun isn't a node.js wrapper. It's an alternative to node.js that sits at roughly the same spot in the stack.
Node.js is a distribution of the V8 JavaScript engine (the thing that executes JavaScript in the Chrome browser), along with a bunch of standard library code written mostly in C++.
Bun is a distribution of the JavaScriptCore engine (the thing that executes JavaScript in the Safari browser), along with a bunch of standard library code written mostly in Zig (and now Rust). Bun's standard library is in many cases compatible with or inspired by the Node.js standard library, but with some changes for convenience and performance.
Answering “who is even using this software” is unfortunately missing in your answer. I am honestly curious. I’ve never seen it “in the wild” (in job descriptions, hearing from past colleagues, meetups etc). Only place I heard about it is HN and Twitter.