Things like Adobe suite and Microsoft office for example. They often have a Linux equivalent but it rarely fits well into industry standard work flows.

I’ve been contemplating forking NextCloud to create a faster, less buggy alternative focusing mostly on the core functionality of office software and storage rather than an ever increasing amount of new modules, but not only would I need a team of developers, I’d also need to monetize it straight out of the gate, because I can’t pay a bunch of developers out of my own pocket. With NextCloud being AGPL, the fork would also be AGPL, of course. And I hate PHP, so this would involve a full backend rewrite to Rust or Go, which also renders the whole thing a pipe dream.