'Fortunately, there's Tox . Like the Signal protocol, Tox is open-source and offers end-to-end encryption. Plus, unlike the Signal protocol, it's peer-to-peer (meaning it doesn't rely on central servers). The "official" Tox messengers also don't require your phone number or access to your contacts.

From my article " How to Avoid Funding the American Deep State ":

and it was founded by a guy whose previous company got sued for privacy violations (among other things).

Since currently none of these Tox messengers are available for all major operating systems, here's a video about the messenger Riot :

(Matrix, the protocol Riot is based on, is not peer-to-peer. And, for the first three years of its development [2014-2017], most of the core contributors worked for Amdocs, which was co-founded by Israeli billionaire Morris Kahn.)

Two more open-source messengers worth mentioning are RetroShare and Kontalk. RetroShare is peer-to-peer and, like Kontalk, available for Android, Linux, MacOS, and Windows.'