Kind of infuriating that the blog post doesn't mention what "Wickr Me" is. The link in the page footer to "Wickr Me" only goes back to the same blog post.
Wickr is/was one(or the only) privacy oriented chat app that didn't require your phone number or your phone book. For some reasons there is no replacement. All the "privacy" messaging apps want your phone number and phone book.
Last I looked Session[0] does not and was created for just that purpose but without sacrificing much in the way if UX.
Briar is another anonymous, fully decentralized chat app. It rides atop Tor rather than reimplementing an anonymous network protocol like Session does.