Love this service!
I use it to send commands and URLs between my devices.
On Linux you can do `ntfy sub` and on android you can have Tasker react when a ntfy notification arrives based on its title and contents. So on just about all my devices I have a background script running that is subscribed to a "DeviceCommands" channel that checks if the Title of new messages contains the device hostname or not. If it does it triggers a script based on the contents of the body.
E.g.:
Title: Pixel8
Message: https://kagi.com
Will automatically send the URL to my browser.
Or:
Title: LivingRoomPC
Message: Shutdown
Will shut down the computer.
For people in the iOS / Apple ecosystem, check Hyperduck which is a neat app to do this