Knit is a location-based messaging concept for iOS which appeared in the App Store from 2014-2016, where it was featured several times in the "Top Messaging Apps" category.
Users were invited to add their friends to the app and begin leaving messages out in the world for them to retrieve. Once their friend was near the note's physical location, they would receive it via Push Notification. This made for a surprising and delightful experience — users were particularly fond of creating scavenger hunts with several steps for their loved ones.
https://www.youtube.com/watch?v=KN9fJlj_Qus
Here is what the tech press had to say about Knit:
"I may very well have just opened up an entirely new medium through which [my wife and I] can send one another passive aggressive notes."
"iOS: Location-based communication is nothing new. Knit, however, lets you target messages to specific people when they arrive at a destination."