I also use "remind me" in Slack a lot as most stuff arrives there. For me it's often just a case of "postpone till after I complete what I'm doing".
I use Google Calendar for appointments, birthdays etc, work wise I'm stuck with Outlook calendar, it's fine, works well to schedule meetings etc.
I always tried to avoid the free-form, text based approach, but I have used a range of tools in the past and they never stuck, for one reason or another. The main ones probably being that they felt incomplete or caused additional stress responses.