Private notes and reminders
Your own notes about someone, and nudges to follow up — never shown to them, ever.
You can keep notes on somebody you have met — where you met, what they are working on, what you promised to send — and set a reminder to follow up.
These are yours alone. The person is never told a note exists, never sees its contents, and nothing about it appears on their side.
Your notes about someone show inside the conversation with them, which is where you need them, and reminders arrive by email when they come due.