Back in the late 80s I knew someone who ran a small company on a Macintosh SE (Mac OS 6 I think) that used a sticky notes app which let you basically comment on any document in any app, and he used it as a quasi-CRM and for notes on sales. Can't remember the name. I vaguely recall him having a crash that corrupted the app's file database, which caused a lot of problems.

He later abandoned it for Borland's Reflex Plus database.