Snackpass is an app which allows customers to order food from local vendors also offering perks once customers amass enough points. This food app powerfully utilizes the influence principle of reciprocity (in terms of exchanging gifts between friends but also in terms of having the app provide an incredible number of discount codes/straight up credit). Relatedly, this app plays on the principle of social proof in that it notifies you if a friend “sends you a gift” (ie. has used the app).