Briar is more or less the gold standard or secure private anonymous messengers. It lacks asynchronous messages and is not very feature rich. I don’t use it much as my more secure devices are frequently offline.
Just installed Briar. Let’s see what all the fuss is about!
Testing is interesting, you will need a group of other users who are prepared to meet in person to verify.
Well I know some of the people on this forum, but I don’t know about meeting in person…