[gabrielsroka]

In HTML

  <button onclick="alert('Hello')">Command1</button>

[jaredcwhite]

Sure, but that's not a native GUI app.

[gaigalas]

Save that as `app.hta` on Windows (from XP up to this day!), then double click it.

Not native GUI, but as fast and useful as one.

It's more limited nowadays, but you can still do a lot.