Javcek Late to the game -- sorry. I have been using the Signal fork Molly.im with success here. Yes, it requires a phone number, because it hooks up to your Signal account. It does, though, offer some features over Signal: it will encrypt your local message archives, for one, and crucially will allow Android-Android linking, which Signal won't -- say you have Signal on a Pixel phone and you want to add your Pixel tablet. Signal doesn't support that, but Molly.im does.