This post is way less informative than the FAQ on your website. I clicked the links thinking I'd get an alternative to JavaFX, Qt, or Electron, but instead I found this which does a better job of explaining what this actually is:

EXT Technical FAQ

What is EXT?

EXT is a platform that allows third party developers to install, load, run, publish and monetize JavaScript-based extensions and native modules, while giving end-users complete control over each extension’s permissions. EXT also includes a store where end-users can find and purchase approved extensions (though the platform also allows side-loading private extensions and modules).

How do extensions work?

Internally, EXT uses the V8 engine to run extensions, which makes their execution extremely fast. Our build pipeline allows us to integrate the latest V8 engine versions automatically, which means you are always going to be up to date with the latest security updates when using EXT. The V8 engine itself does not provide any APIs to extensions, all it can do is run JavaScript code. This is why we allow developers to load EXT modules (which provide functionality) into their extensions. If an extension wants to use an API, it must do so via a module.