While I am writing on an article on COI (Chat over Imap), OpenXchange’s latest hot new stuff, I found a wonderful Wikipedia page: (German) Wikipedia has a great article about messenger services like Whatsapp, Threema, Signal and such. Although the article called “list of mobile instant messenger services” seems to be available only in German, its content is great. Here’s the huge table on functions that might explain why I like to stick with Snowden’s recommendation, Signal.:
By now, I am pretty sure COI will shake this chat world, the concept of using standard mail, mail servers and such as a basis looks very promising against the silos run by American data corporations.