Arguably the biggest non-game applications are in virtual cinematography, architectural visualization, non-game simulations, and immersive art installations. Most of those uses don't result in discrete "apps", though, they're just workflows within Unity designed to produce a specific type of output.
One prominent example of a discrete pro app made from Unity, though, is Digital Monarch Media's filmmaking toolsuite, which is built on Unity.[1] But it fills some unusual hardware and interface needs that Unity is built, or has plugins, to provide (touchscreen interfaces, motion tracking, color grading).
That said, I see non-game apps in the vein of content creation or productivity pop up more frequently now in Godot development than Unity. There are some proof-of-concepts, like the Godello[2] Trello clone that was posted here a while back, but more useful examples are Pixelorama[3], an open-source pixel-art editor built with Godot, and Heavypaint[4], a painting/sketching app.
[1] https://www.vfxvoice.com/instant-feedback-expozure-expands-i...
[2] https://github.com/alfredbaudisch/Godello