Later
Later is a macOS app, that sits in the menubar and helps in creating post-it like reminders.
Usage
Use the What to remind text input to enter the message, that you wish to be reminded later. Next, type in a time in the When to remind field for the notification time - starting from now. Valid identifiers for this text input can be found at the README.
Example
An example might be:
What to remind: Call a colleague back
When to remind: 15 min
You'll get a notification with message Call a colleague back in 15 minutes then.