Plugin for automatic sending of messages

I am working on a plugin that will send messages to WordPress users when a certain event occurs. For example, if a user registers – a welcome message is sent to him. The user has made a purchase and a message is sent to him. The user forgot the items in the cart, a new post was published on the site, etc.
I would like to know from the community:
1) Is there a ready-made plugin with similar functionality? (I did not find)
2) What other fancy features can be added to such a plugin?
3) Will you personally need it?
P.S. The business card page of the future plugin is here https://message-r.com/