I got the Product Hunt email digest about the discussion around ephemeral apps and privacy etc. but checking them all out; none fit my needs.
I'm surprised that Burn Note hasn't taken off more than it has, as it's the best solution for me.
It's cross platform (but desktop first) and when you write a message; you can just generate it as a link, so the receiptant can view (and respond) without needing to sign up for anything or install any apps.
Think about it; if I'm going to send a private message to my lawyer, I'm not exactly going to want to go through the steps of "do you have android or iOS? ok, go and download this app, then add me and I'll send you a message" bla bla like some of these apps make you do. I just want to send them a message saying "check this link".
Product Hunt
Hustle X