I see the author recommended Signal - it's worth noting the German armed forces use a self-hosted Matrix installation! [1]
[2]:
> It is an easy strawman to compare Signal to technology from the 90s and completely ignore IRC and Matrix, especially now that Matrix has started growing: Element recently gained Series B funding of about 30 million, how the French government has completely adopted Matrix in the government and all the German armed forces are connected to Matrix. Even though Matrix is not as well-known as Signal, it is already considered the messaging app of choice for top-secret communications. Matrix offers not only protection for you against a government, their scope is big enough for governments to get protection against other governments.
[2]:
> It is an easy strawman to compare Signal to technology from the 90s and completely ignore IRC and Matrix, especially now that Matrix has started growing: Element recently gained Series B funding of about 30 million, how the French government has completely adopted Matrix in the government and all the German armed forces are connected to Matrix. Even though Matrix is not as well-known as Signal, it is already considered the messaging app of choice for top-secret communications. Matrix offers not only protection for you against a government, their scope is big enough for governments to get protection against other governments.
[1]: https://www.heise.de/newsticker/meldung/Bundeswehr-setzt-kue...
[2]: https://digital-justice.com/articles/skip-signal.html