Retroshare establish encrypted connections between you and your friends to create a network of computers, and provides various distributed services on top of it: forums, channels, chat, mail… Retroshare is fully decentralized, and designed to provide maximum security and anonymity to its users beyond direct friends. Retroshare is entirely free and open-source software. It is available on Android, Linux, MacOS and Windows. There are no hidden costs, no ads and no terms of service.
Maybe. But that “may” is a big MAY, like @IP2@monero.town commented elsewhere. Even for PGP, so classic and so established, “Are there any back doors in PGP?” is FAQ #1.
Absolutely. The developer seems adamant about it too. Pretty Good Privacy is what PGP stands for and that’s the best we can get. Not absolute, not amazing, not extremely good. Pretty good with careful planning can get good enough in most cases. It takes work and it never gets easy sadly.