@jacks, I agree that journals are usually private, but I like the idea of shared journals for many reasons.
The content isn't exposed to the entire internet, just those you've granted permission to via the Day One app.
You own your data, and it's encrypted end-to-end.
Your shared journal could include only IRL friends and family. I would include my wife, kids, parents, and siblings. Maybe a few people from my extended family. That's it.
The viewing experience on Day One is great and it supports multiple attachments and pretty much any file format you can imagine.
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Right now I use group text as a private channel for family, but that's extremely inefficient and aggravating. I think a shared journal would be ideal for this. But I also know that it would be tough to get everyone to use the app.