Just realizing now, "CRUD app" is almost meaninglessly vague - just means an app that reads & writes data, which is almost every app. Calendar, contacts, email client, image editor, blog, comment section, forum - all CRUD apps, as they focus on reading & writing specific types of data.

But obviously there's a world of difference in interface, usability, aesthetics, performance, good writing, security etc. The CRUD part is the simple part.

I guess there's some spectrum between a dumb unspecialized list of table editors ala phpMyAdmin, versus hyper specialized interfaces like game engines that manipulate scene data, triangle data, player inventory, physics entities etc.