ChatSecure is described as 'free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security' and is a popular app in the Social & Communications category. There are more than 50 alternatives to ChatSecure for a variety of platforms, including Android, iPhone, Windows, Linux and Mac. The best alternative is Telegram, which is free. Other great apps like ChatSecure are Signal (Free, Open Source), Element (Free Personal, Open Source), Tox (Free, Open Source) and Jami (Free, Open Source).
Olvid, the most secure messaging app in the world. Olvid guarantees the total and definitive confidentiality of exchanges, relying solely on the mutual trust of interlocutors. For the first time, security does not rely on trusted servers.
Cyph is a secure communication tool designed to be extremely friendly for users of any technical skill level, providing such features as encrypted video calling and file transfers to both individuals and businesses.
With group calls up to 256 users, Video4sure is an easy way to make video calls or setup group meetings. No need to register, install or pay. As soon as you visit the home page, it generates a unique invite link that you can share with your contacts.