Caret is a social app that lives in your phone's address book, shares your phone's sensory data with your friends in the form of your location, where you're going, what you're doing. They call this your "context" which makes those chat messages and calls more relevant. Chat messages are end-to-end encrypted of course!
http://caretapp.com
They recently launched on iOS and have been around for a while on Android with decent reviews. I always used the iPhone "Find Friends" app with my close friends, but now switched to this app: it's much simpler and works across Android and iPhone.
What's cool about Caret is that their APIs also allow developers to share and track location and presence for users & taskers in your food delivery & ride sharing apps! Check out their architecture at https://caret.co/services.html - startups can use these simple APIs and avoid building their own real-time location & status tracking code, which is a pain.
Virgil Security