I use Asana for project management. It’s free (upto 25 users) and its minimal interface/concept makes you more productive.
Well, Asana has this really cool invitation/sharing widget for first time users. I really hate sending annoying invitations for new services I found but this one was something different. See image below and let me know if I’m right.
I have tried to explain my points on the image below. I am not really good with graphics but it should work. In short, It was a good work on smart copy and minimal design.
So if you have an app or service which promotes user invitation, time to think again.