Check it: www.glitch.com/profiles/me/...
How it works: People who visit that page can just start playing (without having to create an account). But, if/when they make an account, we remember whose page they came from. So, during their signup process, they get a little prompt that asks if they want to add you as a friend (since they came in via your link and probably know you) AND we send you an email telling you that they signed up and give you a link to their profile.