I saw during a demo at the Odoo Experience that it was possible to add ad-hoc reminders (not related to a specific document).
For example, I can remind myself to pick up my kids from school.
I also saw this capability described in the Odoo Release Notes at \https://www.odoo.com/odoo-12-release-notes
Reminders
Allow people to add personal reminders in Odoo using the Notes application and the Next Activities modules (ie: lunch with colleagues, call mom,...).
