Delta Chat

Delta Chat is chat that runs on top of email. Rather than building its own network it uses any email account as the pipe. There’s no central server, no phone number and no new account to create. It’s free and open source, with end-to-end encryption handled by Autocrypt. Recent versions cut down metadata leakage by using dedicated chatmail servers. How private it is depends on what carries it. An old mailbox at a logging provider will leak metadata. The strong guarantees only hold on a modern chatmail server with an up-to-date app.