After spending $49 on a crappy baby shower invite sending tool I’m glad to hear this. Could save a lot of people a lot of money! Hopefully it works for non Apple users too.
You need to know your friends' addresses for mail. For both, you have to send out invites individually. People want to make a list of names and phone numbers and send out a blast. They then want a low-effort, centralized place to receive and manage RSVPs.