@one @win10ltsc @BurungHantu
+1 for Threema
@BurungHantu @one @win10ltsc
It does use the open NaCl library and has had a recent audit. https://threema.ch/en/blog/posts/audit19e
If by "not free" you mean you most pay for the app, it's a one time cost of a coffee. I'm willing to support their efforts through paying for the app.