Briar 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?
There are numerous iPhone apps that don't need push notifications and sync just fine.
"Open source programmers do not understand how to code properly for iOS" != "doing things in the background is IMPOSSIBLE on iOS!!!!!"
People just love to screech about iOS/Apple being evil.