On Windows I used to (over 20 years ago) use UltimaShell with the NoteTab text editors. Not all the time, but sometimes. I eventually decided it didn’t help me as much as I thought it would and never re-enabled it, but it was quite a popular tool at that time.
I believe it has since renamed to Intellicomplete Server.
Maybe there’s a Mac equivalent out there? I can’t say I’ve ever looked.