alt Hacker NewsBriar is dead because it doesn't work on iPhones. It doesn't work on iPhones because iOS will only allow waking the app from background when there's a push notification. Push notifications have to go through Apple's servers, which defeats the purpose of a decentralized app where your messages (and metadata) can't be traced.
What about a "fake push" that does not leak message contents, sender etc.? Fuzz the time the push notification is sent by a random amount of time and you have something plausibly private given the constraints?