Briar comes with ways of sharing it offline, so enough for one person to have it.

Most likely how they got it in Iran, as I doubt that critical mass of people had it installed in advance. Most likely doesn't work on iPhones though - no sideloading.

I looked into the iOS issue once, and in the EU at least, it should be possible to add a minimal implementation of the store API to an app, so other iPhones could download the app from an iPhone hosting it.

After discovering the amount of pain involved with that API, I quickly discarded the idea though